Thanks all. The script is php and is rather simple. We've been using it to rotate banners on websites for a few years now.
The advantage of using php vs. flash or animated gifs is that I can add or remove images from the rotation w/o having to remake/recompile the signature.
Most simple web hosting support php. If you rented from godaddy the script would work. Change the php image directory, upload it to the server, upload the images, edit your sig to use the php sig instead of the image file.