var cachedImages = new Array();
    
    function preloadImages() {
      for(var i in imgs) {
        cachedImages[i] = new Image();
        cachedImages[i].src = imgs[i];
      }
    }
    
  function prepareHovers() {
    _prepareHovers(document.getElementsByTagName('img'));
  }
  
  function _prepareHovers(objs) {
    for(var i=0; i<objs.length; i++)
    {     
      var img = objs[i]
      if (img.className == "hoverable")
      {
        img.onmouseover = function () { up(this); }
        img.onmouseout = function () { down(this); }
      }
    }
  }  
  
  function up(img) {
    if (img.src) {
      img.src = img.src.replace('_down', '_up');
    } else {
      img.style.filter = img.style.filter.replace('_down', '_up');
    }
  }
  
  function down(img) {
    if (img.src) {
      img.src = img.src.replace('_up', '_down');
    } else {
      img.style.filter = img.style.filter.replace('_up', '_down');
    }
  }