Here's a dumb question: Why not migrate the machine over the Windows 7 64-bit and use all the RAM you like? I know, Win7 is pricey off the rack, but surely you can access a student package, or talk to your geek friends and see who has an extra license. Heck, I know a guy who just dropped three licenses he wasn't using on another friend. You just have to get hooked up.

Yes, Windows Vista was painful, but 7 makes up for all of that. It really is a lovely OS. Go ahead, make the move.