Hmm... What socket is your CPU? If it is LGA, then keep it. If it is PGA, I'd trash it. Regardless of that, you need new RAM. I would recommend new RAM before a new video card, personally. That's quite slow. Also, I would recommend a new motherboard, since it only has AGP. If it has the PGA socket, then definitely upgrade that (obviously, with a new CPU as well). Then, a new graphics card in PCI-Express format! The HDD could use an upgrade, but you could probably stick with that. And, the PSU is probably okay, if that's the one from ThermalTake. I've heard good things about that one, seems like a steal of a deal for the price they sell it at.
So, basically, I'm saying I would upgrade the whole PC. That way, you'll be futureproofed with Intel. You might possibly want a 7800GT in the mix?