if (document.images)
    {
      preload_image_object = new Image();
      // set image url
      image_url = new Array();
      image_url[0] = "mainslayt/main1.jpg";
      image_url[1] = "mainslayt/main2.jpg";
      image_url[2] = "mainslayt/main3.jpg";
	  image_url[3] = "mainslayt/main4.jpg";
      image_url[4] = "mainslayt/main5.jpg";

       var i = 0;
       for(i=0; i<=4; i++) 
         preload_image_object.src = image_url[i];
    }