if (document.images) 
{
   num_of_images = 5;
   img = new Array();
   for (i=0; i<num_of_images;i++) {
    img[i] = new Image();
   }
   img[0].src = "images/about_us_hover.gif";
   img[1].src = "images/contact_us_hover.gif";
   img[2].src = "images/home_hover.gif";
   img[3].src = "images/mission_statement_hover.gif";
   img[4].src = "images/services_hover.gif";
}