window.addEvent('domready', function() {
 
 
$$('#top_menu li img').each(function(el) {
 
var cloneimg = el.clone().injectAfter(el);
 
var cloneimgsrc = cloneimg.getProperty('src').replace(/^(\S+)\.(gif|jpg|jpeg|png)/, "$1_hover.$2");
 
cloneimg.setProperty('src', cloneimgsrc);
cloneimg.setStyle('opacity','1');
var fx = new Fx.Style(cloneimg,'opacity', {
 duration:800,
 wait:false});
var fx2 = new Fx.Style(cloneimg,'opacity', {
 duration:800,
 wait:false});
 cloneimg.addEvent('mouseenter', function(){
 fx.start(
 '0'
 );
 fx2.stop();
 
 });
 
 cloneimg.addEvent('mouseleave', function(){
 fx2.start(
 '1'
 );
 fx.stop();
 });
});
});