var imgs = {
  "image_1" : "images/res_lg001.jpg",
  "image_2" : "images/res_lg002.jpg",
  "image_3" : "images/res_lg003.jpg",
  "image_4" : "images/res_lg004.jpg"
};
Event.observe(window, "load", function() {
  preloadImages();
});