startList = function() {
  if (document.all && document.getElementById) {
    navRoot = document.getElementById("mainnav");
    for (i=0; i<navRoot.childNodes.length; i++) {
      node = navRoot.childNodes[i];
      if (node.nodeName=="LI") {
        node.onmouseover=function(){this.className+=" over";}
        node.onmouseout=function(){this.className=this.className.replace(/\s*\bover\b/g, "");}
      }
    }
  }
}
window.onload=startList;