window.onload=function(){
var preLoadImagesURL = new Array(
"img/bt_punto_image.jpg",
"img/bt_500_image.jpg");
var preLoadImages =new Array();
var n = preLoadImagesURL.length;
for(i = 0; i < n; i++){
    preLoadImages[i] = new Image();
    preLoadImages[i].src = preLoadImagesURL[i];
}
}