Why do you need a script for this? A very simple, non-Java way to preload images on your splash page is to include them at the bottom of the splash page with a height an width of 1 pixel (so they won't be seen).
Code:
<img src="images/image1.gif" width="1" height="1">
<img src="images/image2.jpg" width="1" height="1">
This will load them into the browser's cache, making them quickly accessible for other pages in your site. Just make sure that you allow enough time before the re-direct for the images to load over a 56k modem. Figure 4KB per second.