I’m going to second [on preview I see it’s actually a third now, but I’ll post this anyways just because] what Enigma said on the case issue. If you ask me, it ranks about even with the video card in terms of importance (Pretty High).
I haven’t built a system myself, only because I can find oodles of stuff to do to a system once it’s already built. That in itself gives me enough to handle that building one (When I bought the last one) seemed a bit daunting- I’d probably still be working on it, if I was left to my own devices.
In my situation, with the case, I pretty much lucked out by choosing a good custom builder- Alienware. Their case is essentially a server case. Actually, after checking it out on the ‘net, it is a server case, albeit one for SOHO applications. Check it out here.
At any rate, in terms of my case, I’m accessing the thing and fiddling around with enough that ease of access has become a big issue. I’m in there three or four times a month, at least. Where I lucked out was in the design and quality of the case. It’s incredibly easy to access, and the parts themselves are well constructed. When I fiddle with a system different from my own, I’m amazed at how hard they are to work around with, and how cheaply they’re designed. It really is a pain to try and work with a crappy case that isn’t designed worth a nickle.
And since you’re building this yourself, you’ll probably be playing around in there as much, if not more, than I am with mine.
Do yourself a favor, and instead of getting lucky like I did, actually know what you’re getting in terms of a case. Play with it- if you can- and see how easily it is to access, to work with, and how user oriented the thing is. Believe me, you’ll curse yourself for skimping out on a case.
Oh, and OS? Definitely go with XP pro. From what I’ve read on people who’ve purchased the home edition, the thing won’t let you do anything, and I mean anything, on your own.
Whatever more that costs, do it.
