seller417 wrote :I believe Windows 7 Ultimate will has a mode to run XP games
+1 to what Hawkeye said. You can use Virtual XP that's available from Microsoft's website to play games that are not supported on Windows 7.
@OP: If you are upgrading to Win7, then I'd make sure that you have at least 2GB RAM especially since you're gaming and also, I'd make sure yo get a 64bit version of Windows. No need to go for Windows 7 Ultimate, as it's just a bit too costly and contains features that most common people won't even use.