function activateMenu() {  
    nav = document.getElementById('top_menu_nav');
	if (document.all && nav.currentStyle) {  
        var navroot = nav;
        var lis=navroot.getElementsByTagName("LI");  
        for (i=0; i<lis.length; i++) {
            if(lis[i].lastChild.tagName == "DIV"){
             	lis[i].onmouseover = function() {this.lastChild.style.display="block"; }
                lis[i].onmouseout=function()    {this.lastChild.style.display="none";}
            }
        }
    }
}