$(function(){
		   $('.roll').each(function(){
									this.originalSrc = $(this).attr('src');
									this.rolloverSrc = this.originalSrc.replace(/(\.gif|\.jpg|\.png)$/,'_on'+"$1");
									this.rolloverImg = new Image();
									this.rolloverImg.src = this.rolloverSrc;
			}).hover(function(){
					$(this).attr('src',this.rolloverSrc);
			},function(){
					$(this).attr('src',this.originalSrc);
			});
});