function initRollOverImages() {
  var image_cache = new Object();
  $("a img.over,input.over").each(function() {
    var imgsrc = this.src;
    var dot = this.src.lastIndexOf('.');
    var imgsrc_ov = this.src.substr(0, dot) + '_ov' + this.src.substr(dot, 4);
    image_cache[this.src] = new Image();
    image_cache[this.src].src = imgsrc_ov;
    var imgTag = this;
    $(this).hover(
      function() { imgTag.src = imgsrc_ov; },
      function() { imgTag.src = imgsrc; });
  });
}

$(document).ready(initRollOverImages);