var preloaded_images = $A();

function init_rollover()
{
  var toggle = function(img){
    return function(){
      if (img.src.match(/_on\./)){
        img.src = img.src.sub(/_on\.(png|gif|jpg)$/, "_off.#{1}");
      } else {
        img.src = img.src.sub(/_off\.(png|gif|jpg)$/, "_on.#{1}");
      }
    }
  };

  var preload = function(img){
    var holder = new Image();
    if (img.src.match(/_on\./)){
      holder.src = img.src.sub(/_on\./, "_off.#{1}");
    } else {
      holder.src = img.src.sub(/_off\./, "_on.#{1}");
    }
    preloaded_images.push(holder);
  };

  var buttons = $$('a.rollover');
  buttons.each(function(button){
    var img = button.getElementsByTagName("img")[0];
    if(img){
      preload(img);
      button.onmouseover = toggle(img);
      button.onfocus = toggle(img);
      button.onmouseout = toggle(img);
      button.onblur = toggle(img);
    }
  });
}

Event.observe(window, "load", init_rollover, false);