function addhover() {
   var navli,i;
   // loop through all elements in the nav
   navli = document.getElementById('centeredmenu').getElementsByTagName('li')
   for(i=0;i<navli.length;i++) {
      // add the hover functions to the li onmouseover and onmouseout
      navli[i].onmouseover=function(){hover(this,'hover');};
      navli[i].onmouseout=function(){hover(this,'');};
   }
}
function hover(o,sClass) {
   if (o) {
      o.className = sClass;
   }
}
addhover();