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