I don't have a GameStop in my city, just an EB Games, and my experience with them is being over charged for used products.
Its not an in-store thing, you order online and they deliver it to your front door. :hehe:
As long as you live in the U.S. that is.
As for the Xbox, I wouldn't recommend it. If your dying to game at this very moment and second, then by all means buy an old, problematic Xbox. If you can wait a little while, wait until your next paycheck and buy a higher quality one.
Or a PS3. Ya' know, cause all the cool kids are buying them.