<script type="text/javascript">
    <!--

    if (document.images)
    {
      preload_image_object = new Image();
      // set image url
      image_url = new Array();
      image_url[0] = "http://mydomain.com/image0.gif";
      image_url[1] = "http://mydomain.com/image1.gif";
      image_url[2] = "http://mydomain.com/image2.gif";
      image_url[3] = "http://mydomain.com/image3.gif";

       var i = 0;
       for(i=0; i<=3; i++) 
         preload_image_object.src = image_url[i];
    }

    //-->
    </script>