$(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);
	});
});