In one of My Layout there are some large images (come from XML) which shown when I mouse hover on some some of the link, but when the Page loads and when i rollover It takes
From http://snipplr.com/view/2122/css-image-preloader
A low-tech but useful technique that uses only CSS. After placing the css in your stylesheet, insert this just below the body tag of your page: Whenever the images are referenced throughout your pages they will now be loaded from cache.
#preloadedImages
{
width: 0px;
height: 0px;
display: inline;
background-image: url(path/to/image1.png);
background-image: url(path/to/image2.png);
background-image: url(path/to/image3.png);
background-image: url(path/to/image4.png);
background-image: url();
}