if (document.images) 
{
   img1 = new Image();
   img2 = new Image();
   img3 = new Image();
   img4 = new Image();
   img5 = new Image();
   img6 = new Image();
   img1.src = "images/header_browse_roll.gif";
   img2.src = "images/header_search_roll.gif";
   img3.src = "images/header_mycollection_roll.gif";
   img4.src = "images/header_about_roll.gif";
   img5.src = "images/header_visit_roll.gif";
   img6.src = "images/header_comment_roll.gif";
}