Just a quick note about the memory: the Mac Pros were pretty infamous for requiring special heat sinks on all the RAM so you may have hit-and-miss luck with RAM pulled out of servers. (Where nobody cares about fan noise and the systems are designed around having the RAM sit in a high-speed wind tunnel.) The 32GB of RAM in mine was intended for use in a Dell 1950/2950 and just has conventional non-finned heat-spreaders on it; the system works okay 99% of the time but I *have* witnessed it hang once or twice; I don't know if that's just coincidence or a heat problem (the fans don't seem to be overspeeding or anything, and ironically the only times it's ever hung are in OS X, not the Linux it usually runs) but I don't recall it ever hanging before it was upgraded from 8GB of heatsink-equipped RAM. Good luck with yours!

Do you have a lead on a video card or do you just plan to do without a "fully working" one? (You *may* be able to get OS X on there using a PC-targeted card, supposedly as long as your card has drivers it will eventually be initialized during the boot process, but you'll be flying blind until then.)