var RollOver = {
  setupRollovers: function() {
    if (!document.getElementsByTagName)
      return;
    var all_links = document.getElementsByTagName('a');
    for (var i = 0; i < all_links.length; i++) {
      var link = all_links[i]; 
      if (link.className &&
          (' ' + link.className + ' ').indexOf(' rollover ') != -1) {
        if (link.childNodes &&
            link.childNodes.length == 1 &&
            link.childNodes[0].nodeName.toLowerCase() == 'img') {
          link.onmouseover = RollOver.mouseover;
          link.onmouseout = RollOver.mouseout;
        }
      }
    }
  },

  find_target: function(e)
  {
    /* Begin the DOM events part, which you */
    /* can ignore for now if it's confusing */
    var target; 

    if (window.event && window.event.srcElement) 
      target = window.event.srcElement;
    else if (e && e.target)
      target = e.target;
    if (!target)
      return null;

    while (target != document.body &&
        target.nodeName.toLowerCase() != 'a')
      target = target.parentNode;

    if (target.nodeName.toLowerCase() != 'a')
      return null;

    return target;
  },

  mouseover: function(e) {
    var target = RollOver.find_target(e);
    if (!target) return;

    // the only child node of the a tag in target will be an img tag
    var img_tag = target.childNodes[0];

    // Take the "src", which names an image called "something.ext",
    // Make it point to "something_over.ext"
    // This is done with a regular expression
    img_tag.src = img_tag.src.replace(/(\.[^.]+)$/, '_over$1');
  },

  mouseout: function(e) {
    var target = RollOver.find_target(e);
    if (!target) return;

    // the only child node of the A-tag in |target| will be an IMG-tag
    var img_tag = target.childNodes[0];

    // Take the "src", which names an image as "something_over.ext",
    // Make it point to "something.ext"
    // This is done with a regular expression
    img_tag.src = img_tag.src.replace(/_over(\.[^.]+)$/, '$1');
  }
}

// When the page loads, set up the rollovers
window.onload = RollOver.setupRollovers;