Hi! Please help!

I am trying to get a certain effect and cannot seem to make it work...

I have a library of 100+ images. I masked out a space on the page, where if the courser rolls over that space, I want the image in the background to change when the cursor moves every 1cm or so ... I want it to be rotate or be a random image from the library (not a 'hotspot' to display a defined image).

Does anyone know of a script or have a solution for this?

THANK YOU!!!