@yoyo, please use real words and complete sentences.

@kerbs I assume you're talking about the mouseovers on the individual product pages (this one, for example)?

It's not difficult. If you're using a javascript library, you can usually write you own in only a few lines. For example (using jQuery):

  <div id="thumbnails">
      <img src="thumb_1.png" alt="thumbnail image for full_1.png" data-img="full_1.png">
      <img src="thumb_2.png" alt="thumbnail image for full_2.png" data-img="full_2.png">
      <img src="thumb_3.png" alt="thumbnail image for full_3.png" data-img="full_3.png">
  </div>
  <img id="full-img" src="full_1.png" alt="full-sized image">

  <script>
  /* this function fires whenever the user mouses over a thumbnail */
  $("#thumbnails img").mouseover(function(){

      /* get the src of the thumbnail's full-size image */
    var imgsrc = $(this).attr("data-img");

    /* get the preview image */
    var big = $("#full-img");

    /* check which image the big image is currently showing -
       if it's different than the thumbnail, we'll show the new image */
    if(imgsrc != big.attr('src')){
        /* hide the big image, change its src, fade it back in. */
      big.hide().attr( {'src':imgsrc} ).fadeIn( 'slow' );
    }
  });
  </script>