Fred, thank you for the input. The dual vs single card I thought 'might' be an issue under linux since most things these days are made specifically for winblows. I would of course like to hear more input on this particular issue. I do play world of warcraft on linux right now but in the future I might consider some other MMO's and if they don't play under linux I would then of course have to resort to a dual boot system. You know of course I'm going to try it with linux first.
I had not considered a second drive since I have a hundreds drives floating around my house. What I did consider however was going with a raptor drive as they are 10k RPMs vs 7200 RPMs. However to do so would be an additional $45 and would only be a 40 gig drive instead of a HUGE 320. Space vs speed.
Looking at your hardware, I see no reason for you to have a problem. I have used the mobo and the graphics card in boxes before without any significant problems.
The only real problem that I found on both the Asus M2N SLI and the Asus M2N32-SLI Deluxe was the sensors. I never did spend the time to try to figure out how to fix it. So Linux couldn't control the fans. But this, for most, is a minor issue.
I do have a couple suggestion though. I have not had good luck with dual graphics cards under linux. They are difficult to get to work and when you do they don't perform that much better than a single card. If this is going to be mostly a Linux box I would suggest upgrading your graphics card to the Nvidia 8600 series and going with just the one card.
If you are thinking about using some of the money saved from above to get a larger hard drive, don't. Two smaller hard drives are more flexible and have other advantages over a single large hard drive.