welcome to auctiva! as a fellow former sder, i think you'll find you'll like it here
like kelbel said, the easy workaround is to host your .gifs offsite on another system until auctiva gets .gif compatability back online.
if you dont have any webspace, photobucket.com will host for free and it's very easy to set up an account there.
dunno if you know, but if you dont need the ability to make a color transparent on a .gif and dont need animation, might consider converting images to .jpg. optimized jpegs are usually smaller and faster to download (which means customer can view more easily).