function sfHover(id) {
	var sfEls = document.getElementById(id).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.onload = function() {
		sfHover('main_nav');
	};
}