its better NOT to buy barebone systems, and its BEST to buy from newegg, NOT tiger direct.
Definitely Socket 939, if ur doing video rendering and stuff, get a Dual core processor, cheapest one is X2 3800+, which you should pick. MOtherboard wise, the best for u, and its cheap, is the MSI K8n Neo4-f, its a GREAT motherboard, and if u ever decide to overclock, its one of the best.
as for graphics, you can just get a x1600 pro or 6600GT or 7600GT.
As for sound card, the Creative X-fI XtremeMusic, thats if ur a sound freak.