I plan on going to something like a 2.6-3.2 quad-core (amd), definitely staying with nvidia though. I had bad experiences with ATI cards. I also plan on throwing another 1tb drive in (or 2 500mb more than likely).
As for ram, I heard that 32 bit windows has a ram limit of 4gb? I ask about it because when I tried to run 64-bit on my current system it just wasn't stable (was getting 0x7f errors, tested ram and it's all good), when I switched to 32-bit, it was back to normal.