if (document.images)
    {
      preload_image_object = new Image();
      // set image url
      image_url = new Array();
      image_url[0] = "green.1.jpg";
      image_url[1] = "yellow.1.jpg";
      image_url[2] = "brown.1.jpgf";
      image_url[3] = "blue.1.jpg";
      image_url[3] = "grey.1.jpg";
      image_url[3] = "red.1.jpg";
      image_url[3] = "blackandwhite.1.jpg";

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