window.onload = function(){

	$$("img.imgroll").each(
		function(obj, i) {        
			obj.addEvent('mouseover', function(){ obj.src = obj.src.replace(/_off/g,'_on'); });
			obj.addEvent('mouseout', function(){ obj.src = obj.src.replace(/_on/g,'_off'); });
		}
	)
}