pdHover = function() {
   var Elements = document.getElementById("mainmenu").getElementsByTagName("LI");
   for (var i=0; i<Elements.length; i++) {
      Elements[i].onmouseover = function() {
         this.className+=" pdHover";
      }
      Elements[i].onmouseout  = function() {
         this.className=this.className.replace(new RegExp(" pdHover\\b"), "");
      }
   }
}

if (window.attachEvent) window.attachEvent("onload", pdHover);