startList = function() {
   if (document.all&&document.getElementById) {
      navRoot = document.getElementById("Menu_ul");
      for (i = 0; i < navRoot.childNodes.length; i++) {
         node = navRoot.childNodes[i];
         if (node.nodeName == "LI") {
            node.onmouseover= function() {
               this.className+=" over";
            }
            node.onmouseout = function() {
               this.className=this.className.replace(" over", "");
            }
         }
      }
   }
}

window.onload = startList;