activateMenu = function(nav) {

 if (document.all && document.getElementById(nav).currentStyle) {
  var navroot = document.getElementById(nav);
  var lis=navroot.getElementsByTagName("LI");
  for (i=0; i<lis.length; i++) {
   if(lis[i].lastChild.tagName=="UL"){
    lis[i].onmouseover=function() {
     this.lastChild.style.display="block";
     }
     lis[i].onmouseout=function() {
     this.lastChild.style.display="none";
    }
   }
  }
 }
}

window.onload= function(){
 activateMenu('menu_ul'); 
}