subHover = function() {
  var subEls = document.getElementById("nav").getElementsByTagName("li");
  for (var i=0; i<subEls.length; i++) {
    subEls[i].onmouseover=function() {
      this.className+=" subhover";
    }
    subEls[i].onmouseout=function() {
      this.className=this.className.replace(new RegExp("subhover\\b"), "");
    }
  }
}
if (window.attachEvent) window.attachEvent("onload", subHover);