Ecco lo script con l'aggiunta di quello per distinguere le varie versioni di IE.
codice:
<SCRIPT language="JavaScript"> 
<!-- 
var OPER=navigator.userAgent.indexOf("Opera"); 
if((OPER>-1)) { 
document.write("<link rel='stylesheet' href='css/opera/opera.css' type='text/css'>"); 
} 
else if (document.all){ // Explorer
{
///Riconosce la versione di IE e carica il CSS adeguato
var x=navigator.appVersion; 
var vers=x.slice(0,3);
switch (vers)
{
case "4.0" : ///IE 4.0
	document.write("<link rel='stylesheet' href='css/ie4.0/ie4.0.css' type='text/css'>"); 	
	break;
case "5.0" : ///IE 5.0
	document.write("<link rel='stylesheet' href='css/ie5.0/ie5.0.css' type='text/css'>");
	break;
case "5.5" : ///IE 5.5
	document.write("<link rel='stylesheet' href='css/ie5.5/ie5.5.css' type='text/css'>");  
	break;
case "6.0" : ///IE 6.0
	document.write("<link rel='stylesheet' href='css/ie6.0/ie6.0.css' type='text/css'>"); 
	break;
default : /// IE Altre versioni
	document.write("<link rel='stylesheet' href='css/ie_other_versions/ie_other_versions.css' type='text/css'>"); 
}
}
} 
else if (document.getElementById){ //Netscape 6 
document.write("<link rel='stylesheet' href='css/netscape/netscape.css' type='text/css'>"); 
} 
//--> 
</SCRIPT>