A very simple Rollover Script is available free from Bravenet. The script includes and example for preloading the images. This helps prevent delays in downloading the roll over images.
The code I linked to, only deals with one button. I read your other posting and know you want two buttons to change. This can be done with a modification of the code I linked to. I created a test page that illustrates the Mouse Over operation. It shows one image, two images that are separate, and then two images that are interlinked. Ignore the fact that the Bravenet site is built into the links.
I should have used images with a more dramatic change, but it still shows the effect. If you use your right mouse button, when you are viewing the page, and select "View Source" you can save the code to your hard drive for examination. The key to making two images change at the same time is multiple statements in the mouse event specifications.
