function activate_menu() {
    var menu = document.getElementById("menu");
    for ( var i = 0; i < menu.childNodes.length; i++ ) {
	if (menu.childNodes[i].className == 'active_menu') {
	    var item = menu.childNodes[i].childNodes[0];
	    var position = "-144px -" + 48 * Math.floor(i / 2) + "px";
	    item.style.backgroundPosition = position;
	    //alert(position);
	    //item.style.backgroundPositionX = "-150px";
	}
    }

}