window.addEvent('domready', function() {
   if($('main_menu')) {
	   var list = $('main_menu').firstChild;
	   var menu = $(list).getChildren('li');
	   menu.each(function(el){
	      el.addEvents({
	         'mouseenter': function(){
	            this.getFirst('ul').setStyle('display','block');
	         },
	         'mouseleave': function(){
	            this.getFirst('ul').setStyle('display','none');
	         }
	      });

	   });
   }
});