im going to throw my two cents in just because you might want some extra options
i recently built the following system for a workstation computer;
a64 X2 3800+
80 gig western digital SATA hdd
2 gigs of adata vitesta pc3200 ram (make it a gig, put the money into higher quality overclocking ram and maybe even save a few bucks)
ati firegl v5000 pci-e...
i suggest switching the video card to something more oriented for gaming rather than workstation work (vcard is the big difference between a workstation and a gaming rig)
a single x1900xt or x1900xtx would survive for 2-3 years if you dont want to max the settings constantly
and yes, this is prolly more than youre willing to spend...
600$ for everything minus the video card
prolly what... 400-600 for the video card? (all USD)
also, the processor would be able to overclock really really well with stock cooling, like 2.5 ghz stable at least. look for some good ddr500 ram and there you go, insta-performance increase once you get any grinches worked out.
i may be totally off base on this post as I just skimmed through and im tired, but good luck with whatever you plan on doing.