Based on the above, it sounds like building this system wouldn't be worth it, given that it would also be possible to build separate systems that would provide greater performance anyway, especially if I can use Intel processors. As I mentioned above, I wanted to use AMD CPUs because I could fit AM2 heatsinks to Socket F, but I couldn't find any LGA771 boards that would accept LGA775 heatsinks.
We're still going to build some sort of system, but I think we'll try to kludge it together from parts on hand, so it won't be a high performance box. I'm looking into GPU folding, as I have an 8800GT now.
Athlon64 3000+ @ 2.6 GHz, Radeon 9550, Seasonic S12-380, Zalman CNPS7000-Cu, Yate Loon 120mm, Centurion 5 case
Core2Duo E6320 @ 2.4GHz, Seasonic S12-330, Zalman CNPS7000-AlCu, Yate Loon 120mm, Ultra MicroFly