se tralasci l' animazione è leggero e crossbrowser
codice:
<html> 
<head> 
<title></title> 
<script type="text/javascript"> 
function mmenu(ID) { 

var menu = document.getElementById(ID); 
var display = menu.style.display; 

menu.style.display = (display == "block") ? "none" : "block"; 

var nodoUL=document.getElementById(ID).parentNode.parentNode; 
var nodo=nodoUL.childNodes; 

for (var i=0;i<nodo.length;i++) { 

if ((nodo[i].tagName=="LI")&&(nodo[i].hasChildNodes())) { 

for (var j=0;j<nodo[i].childNodes.length;j++) { 
if((nodo[i].childNodes[j].tagName=="UL")&&(nodo[i].childNodes[j].id!=ID)) { 
nodo[i].childNodes[j].style.display="none"; 
} 
} 
} 
} 


} 


/* inizializzazione del menu */ 

window.onload = function() { 
var uls = document.getElementsByTagName("ul"); 
for (i=0;i<uls.length;i++) { 
if(uls[i].getAttribute("class")=="submenu")uls[i].style.display = "none"; 
if(uls[i].getAttribute("id") && uls[i].getAttribute("id").search("submenu-")!= -1) uls[i].style.display = "none"; 
} 
} 

</script>
</head>
<body>


 

 
<ul> 
<li class="menu">Main 
<ul class="submenu" id="submenu-1"> [*]Home [*]Disclaimer [/list]
 
<li class="menu">Roms 
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<li class="menu">Emulatori 
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<li class="menu">Midi 
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<li class="menu">Video 
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<li class="menu">Sfondi 
<ul class="submenu" id="submenu-7"> [*]800x600 [*]1024x768 [/list]
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</p>
</body> 
</html>
ciao