startList = function() {
  var Els = document.getElementById("menu").getElementsByTagName("LI");
  for (var i=0; i<Els.length; i++) {
    Els[i].onmouseover=function() {
      this.className+=" over";
    }
    Els[i].onmouseout=function() {
      this.className=this.className.replace(new RegExp(" over\\b"), "");
    }
  }
}
window.onload=startList;