Since you want to play games, obviously Linux is out of the question. Windows XP or Vista is what you want. If you've already stated you don't want Vista, then that leaves you with your only option: Windows XP. I'd get the 32-bit edition. If you want 64-bit, just go with Vista.
That motherboard supports SATA3.0, so any SATA3.0 drive would be fine.
I'd get a Seagate 7200.10 or 7200.11 drive. Almost any of them
will be fine. The 7200.11 are a little better because of the 32MB cache, but a 16MB wouldn't be bad either.