not sure you have the cash right now, but i built myself a computer for 500 bucks(includes part shipping) you just have to carry over a few parts(soundcard, vidcard, moniter was all)
that was like 5 months ago, prices have gone way down.
i figure if i was going to upgrade today i would go with this:
mobo: shuttle ak71 - $102, had DDR mem support
CPU: 1.2ghz tbird athlon AXIA stepping - $115 shipped
Ram: 256 PC2100 DDR - 55 shipped from crucial
Fan: something good, ask in correct forum - $20
Case: Enlight 7237 - 40 shipped w/ 300watt psp
102+115+55+20+40 = 332
so for 350 you can get a top of the line computer. just something to think about, just upgrade the vidcard later, soundcard...who cares 🙂