[quote name='JackFlash81']I have heard that Walmart is really the only retailer that will do an exchange without a receipt.
True?[/QUOTE]
It depends. I've done it with gifts before without too many hassles (they will log your ID to make sure you aren't doing it constantly) but other times I've been denied. YMMV.
To your credit (or the OPs credit, can't remember his name atm), if all you're trying to do is swap one format for another (not changing the game and/or wanting cash back), you might have a better than average chance.
Just go, politely explain your situation and see if they'll help you out.
All that aside, the PS3 version isn't terrible. I went...
Fallout 3 (360) ----> Fallout 3 (PS3) ----> Fallout 3 GOTY (360) and didn't notice any glaring differences. Fallout 3 on PS3 didn't crash for me at all.