var preload = new Array('/images/navigation/product_on.gif', '/images/navigation/story_on.gif', '/images/navigation/news_on.gif', '/images/navigation/shop_on.gif', '/images/navigation/contact_on.gif');

var loader = new Array();
for(var i = 0; i < preload.length; i++){
   loader[i] = new Image();
   loader[i].src = preload[i];
}