If you're looking into buying a PC that will last for a while, I'd say go for the more 'advanced' stuff, like 64bit, a decent 3D card (not SLI, that's a bit too extreme
) and a decent amount of RAM (say, 1.5GB). That way you're ready for the new OS (Vista, I'm assuming you're looking into a PC, not Mac?). My 'old' PC (read: before I switched to Mac) had 2GB RAM, a 2.1Ghz AMD Athlon64 (64bit) and an ATI Radeon X800something. basically both the CPU and video card are already 'outdated', but they performed great. And by great, I really mean 'anything I could throw at it worked like a charm' great. Not trying to brag here (like I can, don't even own the PC anymore
), but I'm just saying that looking into that direction might be ideal for you. You'll be ready for Vista, should you want to upgrade later on, and you're not looking at extremely expensive stuff.
Oh, and think big when it comes to hard drive space. I miscalculated EVERY time I bought a new one, and now I'm running with a total of 650GB on my main computer and I FINALLY feel at ease. For now...