function rolloverImg() {
	if(document.getElementsByTagName) {
		var images = document.getElementsByTagName("img");

		for(var i=0; i < images.length; i++) {
			if(images[i].getAttribute("src").match("_roff.")){
				imgsrc = images[i].getAttribute("src").replace("_roff.", "_ron.");
				//alert(imgsrc);
				imgPreload(["imgsrc"]);
				images[i].onmouseover = function() {
					this.setAttribute("src", this.getAttribute("src").replace("_roff.", "_ron."));
				}
				images[i].onmouseout = function() {
					this.setAttribute("src", this.getAttribute("src").replace("_ron.", "_roff."));
				}
			}
		}
	}
}

if(window.addEventListener) {
	window.addEventListener("load", rolloverImg, false);
}
else if(window.attachEvent) {
	window.attachEvent("onload", rolloverImg);
}

function imgPreload(imgs){
 for(var i = 0; i < imgs.length; i++){
   var imgObj = new Image();
   imgObj.src = imgs[i];
 }
}