function SetRollovers() {

  // Set rollover images and preload them.

  // Idea for 'preloads' object from
  // http://www.quirksmode.org/js/newmouseover.html
  var preloads = new Object();
  var lim = document.images.length;

  var i;
  for(i=0; i<lim; i++) {
    var im = document.images[i];
    if (im.src.match(/_verde/)) {    // If image is a rollover.
      var off = im.src;
      var on = im.src.replace(/_verde/, "_rojo");

      preloads[off] = new Image;
      preloads[off].src = on;
      preloads[on] = new Image;
      preloads[on].src = off;

      im.onmouseover = function () { this.src = preloads[this.src].src; }
      im.onmouseout = function () { this.src = preloads[this.src].src; }
    }
  }

}