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

  for(var i=0; i < images.length; i++) {
   if(images[i].getAttribute("src").match("_out."))
   {
    images[i].onmouseover = function() {
     this.setAttribute("src", this.getAttribute("src").replace("_out.", "_on."));
    }
    images[i].onmouseout = function() {
     this.setAttribute("src", this.getAttribute("src").replace("_on.", "_out."));
    }
   }
  }
 }
}

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