我找的代码如下:
<SCRIPT language=jscript>
var mmenus = new Array();
var misShow = new Boolean();
misShow=false;
var misdown = new Boolean();
misdown=false;
var msrcel;
var mfromel;
var mtoel;
var musestatus=false;
var mthestatus="";
var mpopTimer = 0;
mmenucolor='#009AFF';mfontcolor='#FFFFFF';mmenuoutcolor='#009AFF';mmenuincolor='#009AFF';mmenuoutbordercolor='#009AFF';mmenuinbordercolor='#009AFF';mmidoutcolor='#0099FF';mmidincolor='#0099FF';mmenuovercolor='#FF0000';mitemedge='0';msubedge='1';mmenuunitwidth=60;mmenuitemwidth=160;mmenuheight=22;mmenuwidth='500';mmenuadjust=10;mmenuadjustV=0;mfonts='font-family: 宋体; font-size: 9pt; color: #FFFFFF; ';mcursor='default';

function stoperror(){
return true;
}
window.onerror=stoperror;
function mpopOut() {
mpopTimer = setTimeout('mallhide()', 500);
}
function getReal(el, type, value) {
    temp = el;
    while ((temp != null) && (temp.tagName != "BODY") {
        if (eval("temp." + type) == value) {
            el = temp;
            return el;
        }
        temp = temp.parentElement;
    }
    return el;
}


function mMenuRegister(menu)
{
mmenus[mmenus.length] = menu
return (mmenus.length - 1)
}
function mMenuItem(caption,command,target,isline,statustxt,img,sizex,sizey,pos){
    this.caption=caption;
    this.command=command;
    this.target=target;
    this.isline=isline;
    this.statustxt=statustxt;
    this.img=img;
    this.sizex=sizex;
    this.sizey=sizey;
    this.pos=pos;
}
function mMenu(caption,command,target,img,sizex,sizey,pos){
    this.items = new Array();
    this.caption=caption;
    this.command=command;
    this.target=target;
    this.img=img;
    this.sizex=sizex;
    this.sizey=sizey;
    this.pos=pos;
    this.id=mMenuRegister(this);
}
function mMenuAddItem(item)
{
this.items[this.items.length] = item
item.parent = this.id;
this.children=true;
}

mMenu.prototype.addItem = mMenuAddItem;
function mtoout(src){

src.style.borderLeftColor=mmenuoutbordercolor;
src.style.borderRightColor=mmenuinbordercolor;
src.style.borderTopColor=mmenuoutbordercolor;
src.style.borderBottomColor=mmenuinbordercolor;
src.style.backgroundColor=mmenuoutcolor;
src.style.color=mmenuovercolor;
}
function mtoin(src){

src.style.borderLeftColor=mmenuinbordercolor;
src.style.borderRightColor=mmenuoutbordercolor;
src.style.borderTopColor=mmenuinbordercolor;
src.style.borderBottomColor=mmenuoutbordercolor;
src.style.backgroundColor=mmenuincolor;
src.style.color=mmenuovercolor;
}
function mnochange(src){
src.style.borderLeftColor=mmenucolor;
src.style.borderRightColor=mmenucolor;
src.style.borderTopColor=mmenucolor;
src.style.borderBottomColor=mmenucolor;
src.style.backgroundColor='';
src.style.color=mfontcolor;

}
function mallhide(){
    for(var nummenu=0;nummenu<mmenus.length;nummenu++){
        var themenu=document.all['mMenu'+nummenu]
        var themenudiv=document.all['mmenudiv'+nummenu]
mnochange(themenu);
mmenuhide(themenudiv);
}
}
function mmenuhide(menuid){
menuid.style.filter='Alpha(Opacity=100)';
menuid.style.visibility='hidden';
misShow=false;
}
function mmenushow(menuid,pid){
menuid.style.filter='Alpha(Opacity=80)';
menuid.style.left=mposflag.offsetLeft+pid.offsetLeft+mmenuadjust;menuid.style.top=mposflag.offsetTop+mmenutable.offsetHeight+mmenuadjustV+1;
if(mmenuitemwidth+parseInt(menuid.style.left)>document.body.clientWidth)
menuid.style.left=document.body.clientWidth-mmenuitemwidth;
menuid.style.visibility='visible';
misShow=true;
}
function mmenu_over(menuid,x){
mtoel = getReal(window.event.toElement, "className", "coolButton";
mfromel = getReal(window.event.fromElement, "className", "coolButton";
if (mtoel == mfromel) return;
msrcel = window.event.srcElement;
if(x<0){
misShow = false;
mallhide();
mtoout(msrcel);
}else{

mallhide();
mtoin(msrcel);
mmenushow(menuid,eval("mMenu"+x));

}
clearTimeout(mpopTimer);
}
function mmenu_out(menuid){
mtoel = getReal(window.event.toElement, "className", "coolButton";
mfromel = getReal(window.event.fromElement, "className", "coolButton";
if (mtoel == mfromel) return;    
msrcel = window.event.srcElement;
if (misShow){
mtoin(msrcel);
}else{
mnochange(msrcel);
}
mpopOut()
}
function mmenu_down(menuid,x){
msrcel = getReal(window.event.srcElement, "className", "coolButton";
if(misShow){
mmenuhide(menuid);
mtoout(msrcel);
}
else{
mtoin(msrcel);
mmenushow(menuid,eval("mMenu"+x));
misdown=true;
}
}
function mmenu_up(){
misdown=false;
}
function mmenuitem_over(menuid){
msrcel = getReal(window.event.srcElement, "className", "coolButton";
if(misdown){
    mtoin(msrcel);
}
else{
mtoout(msrcel);
}
if(mthestatus!=""{
    musestatus=true;
    window.status=mthestatus;
}
clearTimeout(mpopTimer);
}
function mmenuitem_out(menuid){
msrcel = getReal(window.event.srcElement, "className", "coolButton";
mnochange(msrcel);
if(musestatus)window.status="";
mpopOut()
}
function mmenuitem_down(menuid){
msrcel = getReal(window.event.srcElement, "className", "coolButton";
mtoin(msrcel)
misdown=true;
}
function mmenuitem_up(menuid){
msrcel = getReal(window.event.srcElement, "className", "coolButton";
mtoout(msrcel)
misdown=false;
}
function mexec2(x){
var cmd;
if(mmenus[x].target=="blank"{
cmd = "window.open('"+mmenus[x].command+"')";
}else{
cmd = mmenus[x].target+".location='"+mmenus[x].command+"'";
}
eval(cmd);
}
function mexec(x,i){
var cmd;
if(mmenus[x].items[i].target=="blank"{
cmd = "window.open('"+mmenus[x].items[i].command+"')";
}else{
cmd = mmenus[x].items[i].target+".location='"+mmenus[x].items[i].command+"'";
}
eval(cmd);
}
function mbody_click(){

if (misShow){
    msrcel = getReal(window.event.srcElement, "className", "coolButton";
    for(var x=0;x<=mmenus.length;x++){
        if(msrcel.id=="mMenu"+x)
        return;
    }
    mallhide();
}
}
document.onclick=mbody_click;
var mMenuBodyRef;
function mwritetodocument(){
var mwb=1;
for(var i in document.all){
if (document.all[i].tagName == 'BODY'){
mMenuBodyRef = document.all[i]
var stringx='<div id="mposflag" style="position:absolute;"></div><table id=mmenutable border=0 cellpadding=0 cellspacing=2 width='+mmenuwidth+' height='+mmenuheight+' bgcolor='+mmenucolor+
' onselectstart="event.returnvalue=false"'+
' style="filter:Alpha(Opacity=80);cursor:'+mcursor+';'+mfonts+
' border-left: '+mwb+'px solid '+mmenuoutbordercolor+';'+
' border-right: '+mwb+'px solid '+mmenuinbordercolor+'; '+
'border-top: '+mwb+'px solid '+mmenuoutbordercolor+'; '+
'border-bottom: '+mwb+'px solid '+mmenuinbordercolor+'; padding:0px"><tr>'
for(var x=0;x<mmenus.length;x++){
    var thismenu=mmenus[x];
    var imgsize;
     if(thismenu.sizex=="0"&&thismenu.sizey=="0"{
     imgsize="";
     }else{
     imgsize=" width="+thismenu.sizex+" height="+thismenu.sizey;
     }
    var ifspace;
     if(thismenu.caption==""{
     ifspace="";
     }else{
     ifspace=" ";
     }
    stringx += "<td class=coolButton id=mMenu"+x+" style='border: "+mitemedge+"px solid "+mmenucolor+
    "' width="+mmenuunitwidth+"px onmouseover=mmenu_over(mmenudiv"+x+
    ","+x+" onmouseout=mmenu_out(mmenudiv"+x+
    " onmousedown=mmenu_down(mmenudiv"+x+","+x+"";
     if(thismenu.command!=""{
     stringx += " onmouseup=mexec2("+x+";mmenu_up();";
     }else{
          stringx += " onmouseup=mmenu_up()";
     }
     if(thismenu.pos=="0"{
     stringx += " align=center><img align=absmiddle src="+thismenu.img+imgsize+">"+ifspace+thismenu.caption+"</td>";    
     }else if(thismenu.pos=="1"{
     stringx += " align=center>"+thismenu.caption+ifspace+"<img align=absmiddle src="+thismenu.img+imgsize+"></td>";    
     }else if(thismenu.pos=="2"{
     stringx += " align=center background="+thismenu.img+">"+thismenu.caption+"</td>";    
     }else{
     stringx += " align=center>"+thismenu.caption+"</td>";
     }
    stringx += "";
}
stringx+="<td width=*> </td></tr></table>";


for(var x=0;x<mmenus.length;x++){
    thismenu=mmenus[x];
if(x<0){
stringx+='<div id=mmenudiv'+x+' style="visiable:none"></div>';
}else{
stringx+='<div id=mmenudiv'+x+
' style="filter:Alpha(Opacity=80);cursor:'+mcursor+';position:absolute;'+
'width:'+mmenuitemwidth+'px; z-index:'+(x+100);
if(mmenuinbordercolor!=mmenuoutbordercolor&&msubedge=="0"{
stringx+=';border-left: 1px solid '+mmidoutcolor+
';border-top: 1px solid '+mmidoutcolor;}
stringx+=';border-right: 1px solid '+mmenuinbordercolor+
';border-bottom: 1px solid '+mmenuinbordercolor+';visibility:hidden" onselectstart="event.returnvalue=false">\n'+
    '<table width="100%" border="0" height="100%" align="center" cellpadding="0" cellspacing="2" '+
    'style="'+mfonts+' border-left: 1px solid '+mmenuoutbordercolor;
if(mmenuinbordercolor!=mmenuoutbordercolor&&msubedge=="0"{
    stringx+=';border-right: 1px solid '+mmidincolor+
    ';border-bottom: 1px solid '+mmidincolor;}
    stringx+=';border-top: 1px solid '+mmenuoutbordercolor+
    ';padding: 4px" bgcolor='+mmenucolor+'>\n'
    for(var i=0;i<thismenu.items.length;i++){
        var thismenuitem=thismenu.items[i];
        var imgsize;
     if(thismenuitem.sizex=="0"&&thismenuitem.sizey=="0"{
     imgsize=""
     }else{
     imgsize=" width="+thismenuitem.sizex+" height="+thismenuitem.sizey
     }
     var ifspace;
     if(thismenu.caption==""{
     ifspace="";
     }else{
     ifspace=" ";
     }
        if(!thismenuitem.isline){
        stringx += "<tr><td class=coolButton style='border: "+mitemedge+"px solid "+mmenucolor+
        "' width=100% height=15px onmouseover=\"mthestatus='"+thismenuitem.statustxt+"';mmenuitem_over(mmenudiv"+x+
        ";\" onmouseout=mmenuitem_out(mmenudiv"+x+
        " onmousedown=mmenuitem_down(mmenudiv"+x+" onmouseup=";
                stringx += "mexec("+x+","+i+";mmenuitem_up(mmenudiv"+x+" ";
                if(thismenuitem.pos=="0"{
     stringx += "><img align=absmiddle src="+thismenuitem.img+imgsize+">"+ifspace+thismenuitem.caption+"</td></tr>";    
     }else if(thismenuitem.pos=="1"{
     stringx += ">"+thismenuitem.caption+ifspace+"<img align=absmiddle src="+thismenuitem.img+imgsize+"></td></tr>";    
     }else if(thismenuitem.pos=="2"{
     stringx += "background="+thismenuitem.img+">"+thismenuitem.caption+"</td></tr>";    
     }else{
     stringx += ">"+thismenuitem.caption+"</td></tr>";
     }
                }else{
        stringx+='<tr><td height="1" background="hr.gif"><img border="0" src="none.gif" width="1" height="1"></td></tr>\n';
        }
    }stringx+='</table>\n</div>'
    }
    
}

document.write("<div align='left'>"+stringx+"</div>";
break
}
}
}


function document_load(){
    mwritetodocument();


}mpmenu1=new mMenu('文件','','self','','','','');
mpmenu1.addItem(new mMenuItem('新建','javascript:alert("新建"','self',false,'新建','','','',''));
mpmenu1.addItem(new mMenuItem('打开','javascript:alert("打开"','self',false,'打开','','','',''));
mpmenu1.addItem(new mMenuItem('保存','javascript:alert("保存"','self',false,'保存','','','',''));
mpmenu1.addItem(new mMenuItem(null,null,null,true));
mpmenu1.addItem(new mMenuItem('退出','javascript:alert("退出"','self',false,'退出','','','',''));
mpmenu2=new mMenu('编辑','','self','','','','');
mpmenu2.addItem(new mMenuItem('撤销','javascript:alert("撤销"','self',false,'撤销','','','',''));
mpmenu2.addItem(new mMenuItem('重做','javascript:alert("重做"','self',false,'重做','','','',''));
mpmenu2.addItem(new mMenuItem(null,null,null,true));
mpmenu2.addItem(new mMenuItem('拷贝','javascript:alert("拷贝"','self',false,'拷贝','','','',''));
mpmenu2.addItem(new mMenuItem('粘贴','javascript:alert("粘贴"','self',false,'粘贴','','','',''));
mpmenu3=new mMenu('收藏','','self','','','','');
mpmenu3.addItem(new mMenuItem('我的主页','http://www.tastelife.net','blank',false,'访问我的主页','','','',''));
mpmenu3.addItem(new mMenuItem('Yahoo','http://www.yahoo.com','blank',false,'访问Yahoo','','','',''));
mpmenu4=new mMenu('帮助','','self','','','','');
mpmenu4.addItem(new mMenuItem('内容','javascript:alert("内容"','self',false,'内容','','','',''));
mpmenu4.addItem(new mMenuItem('给我写email','mailto:webmaster@tastelife.net','self',false,'给我写email','','','',''));
mpmenu4.addItem(new mMenuItem(null,null,null,true));
mpmenu4.addItem(new mMenuItem('关于','javascript:alert("关于"','self',false,'关于这个软件','','','',''));

</SCRIPT>
<SCRIPT>document_load()</SCRIPT>需要改哪才能实现下拉菜单在不同分辨率下都居中?先谢谢了!