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