Changing Win XP to 7

[FooFighter]

Bad idea. Baaaad idea.

XP is still superior to 7, no matter what they say. Yes, 7 is less annoying than Vista, that's true, and yes, it also allows you to play DirectX10 games and add more RAM to your rig. But - ignoring the fact that you don't really need more than 2 gigs of RAM for gaming - you can emulate DX10 pretty nicely under XP already, and if you switch to XP 64, you can also pop in more RAM without having to put up with an extremely annoying, insecure, phoning-home OS like 7.

If you want better performance in games, I recommend going for a better GPU instead. Check out the GeForce 8800 - it's a bit pricey, but an extremely good graphics card and one you can trust to last for a while.