Navagon: Which bit? The save game corruption is apparently standard. Try backing up your saves and then reinstalling the game. Saves won't work. They're encrypted by GFWL so you can only use them with that install.
They work, I have moved my GFWL offline save from computers and Windows install to Windows install several time and never had any issue, the only thing you have to do is to make sure you copy your saves AND the Live something folder which contains the encryption key of your offline profile.
StingingVelvet: Use offline profiles, I don't think they mess with those saves. That's what I do, never had a problem.
Offline profiles are encrypted too, if you don't backup/restore the profile along with the encryption key you won't be able to load the saves on another Windows install.
Unless of course they changed that recently, the last GFWL game I played being Dead Rising 2.