I'll double the recommendation for a 270. You might be able to pick up used ones for ~$125. Make sure your PSU can handle it, though.
I have a nice Antec power supply. Got it for free. I pick up computer parts like that here and there, free or really cheap.
"Megatower 2000" is long overdue for an overhaul (it's not my main use box currently). Originally built in 2000 (I had a decent amount of $ saved, ohhh the system I could build now for what it cost!) as a super fast Pentium III in a 12 bay case, the case is all that's left of the original build. Currently has a dual core Socket 939 Athlon, 2.5 gig DDR1 and around 0.75TB total storage in six hard drives.
The 9800 GT card was in MT2000 but it never worked right, random freezes, apparently it just isn't quite 100% backwards sympatico with PCIe 1.0. Been months since I used the old thing, grabbed the GT card to replace the even older 512 meg ATi 4200 HD Pro card that was in the box I'm using right now.
I've kicked myself for not doing that much much sooner when the 9800 GT would have been usable in the early days of Bitcoin.
