function imgRollover() {
if(document.getElementsByTagName) {
var images = document.getElementsByTagName("img");
var imglength = images.length;
var image_cache = {};
for(var i=0; i < imglength; i++) {
if(images[i].className=="btn"){
var imgsrc = images[i].getAttribute("src");
if(!image_cache[imgsrc]){
image_cache[imgsrc] ={};
image_cache[imgsrc]['over'] = new Image();
image_cache[imgsrc]['over'].src = imgsrc.replace("_out.", "_over.");
}

images[i].onmouseover = function() {
this.setAttribute("src", this.getAttribute("src").replace("_out.", "_over."));
}
images[i].onmouseout = function() {
this.setAttribute("src", this.getAttribute("src").replace("_over.", "_out."));
}
}
}
}
}
if(window.addEventListener) {
window.addEventListener("load", imgRollover, false);
}else if(window.attachEvent) {
window.attachEvent("onload", imgRollover);
}