function imgRollover() {
	
	//swap img
  var conf = {className : 'btn',postfix : '_on'};
  var image_cache = new Object();
  $('img.'+conf.className).each(function(i) {
		var imgsrc = this.src;
		var dot = this.src.lastIndexOf('.');
		var imgsrc_on = this.src.substr(0, dot) +  conf.postfix + this.src.substr(dot, 4);
		image_cache[this.src] = new Image();
		image_cache[this.src].src = imgsrc_on;
		$(this).hover(function() { this.src = imgsrc_on;},function() { this.src = imgsrc; });
	});
	
}
if(window.addEventListener) {
window.addEventListener("load", imgRollover, false);
}else if(window.attachEvent) {
window.attachEvent("onload", imgRollover);
}