Cool! Looks like I have a new thread to haunt!

Sooo... my first though is to use a single image for the background and then use the "sliding door" method to change image's Position. This is actually faster than swapping out two images. I have actually done this quite a bit and it isn't hard to do, but will take a bit of study to make sure it fits in well with zencart and uses zencarts css identifiers.