Umm, you can play some windows games with Linux via winex. Its $5 per month though. Linux itself doesn't have a problem with Virii, but if you're using Wine, it can catch them. If you are asking for the best distro for gaming, I'd say Gentoo. But don't try it until you've learnt your way around Linux. Go with Mandrake out of the ones you said. RH support is discontinued, and Mandrake has been much better suited to desktop use for a few releases now.
As for the drivers, NVidia publishes drivers for Linux, and they work very well. The AC97 sound will probably work. Could have told you for sure if you had said the chip itself rather than the codec.
The motherboard should also work. Mandrake will detect most hardware and set it up for you. Then all you need to do is download the NVidia drivers and FOLLOW THE INSTRUCTIONS.
I'd advise you to dual boot for a bit, from the sounds of it you haven't quite got the idea about Linux. Whilst its great, it isn't for everyone, and many gamers end up dual booting for games. Linux is stable, but remember that Windows programs are often released with many bugs etc.
Anyway - by all means try it! You'll probably like it