The main thing that seems to be "universal", is that whatever you get needs to be very, very Open GL oriented. After that.... well.... mostly NVidia based, though some  are having  reasonable luck with ATI, lately.  Vid-card / renders... well, the vid-card only handles , so to speak, what is on your monitor... renders are RAM  and CPU intensive.... how much, and how fast, govern how soon you complete a render... One thing to consider before you go haring off to buy a dual dual-core motherboard... there are STILL a major number of applications that can't work with dual-core, let alone a dual CPU. The pain in the fundament is that, no dual core = nothing over 2 GIG of RAM. Lovely catch-22, that. Lou.

"..... and that was when things got interestiing."