function rollover() {
  if (!document.getElementById) return
  var imgOrSrc;
  var imgPreload = new Array();
  var images = document.getElementsByTagName('img');
  for (var i = 0; i < images.length; i++) {
    if (images[i].getAttribute('rsrc')) {
      imgPreload[i] = new Image();
      imgPreload[i].src = images[i].getAttribute('rsrc');
      images[i].onmouseover = function() {
        imgOrSrc = this.getAttribute('src');
        this.setAttribute('src',this.getAttribute('rsrc'))
      }
      images[i].onmouseout = function() {
        this.setAttribute('src',imgOrSrc)
      }
    }
  }
}

if (window.addEventListener)
 window.addEventListener('load', rollover, false);
else if (window.attachEvent)
 window.attachEvent('onload', rollover);