very nice built but try getting a full tower with many fans...it will help you cool down your videocard and will extend the life of your equipment..the processor is good but a little overclock will help....the motherboard is also good but try going with DFI they make the best and the most stable motherboards, in my opinion( i do like gigabyte boards but 2 of them quit on me as i pushed em 2 far apparently the model was 965p ds3..but my DFI is going far and beyond, your milage might vary).you can get better ram but it will cost a bit more...the powersupply is excellent and will handle your videocard hope it helps, also if you are going to get 2 video cards in future get a 850+ watt powersupply with >80% efficency
* Is the processor I've selected fast enough to support the video card http://en.wikipedia.org/wiki/Video_card ?
It will run 1 card fine. However, 2 the CPU may bottleneck the 2nd card. An overclock to 4 ghz + will help with the dual core CPU. Another option is a use a fast quad core and give it a little overclock.
* Is the motherboard a good fit for this video card? Is there a better choice?
Motherboard looks fine and will support a second card down the road no problems.
* Given the absurd power requirements of this card, is there a power supply I could buy to one day support a second card?
Buy a Corsair 1000 watt. Cheaper than the rest and from all reviews Ive seen thus far its a very good PSU. As Prox suggested the PCP&C PSU is a fine PSU as well, just slightly more expensive.
* Barring that, what is a good PSU to support just this one card?
See last statement.
The rest of the build looks fine. Id consider changing the ram to maybe Corsair, Mushkin, or Kingston. Ive never used A-Data, so I cant pass judgment on how good a product your getting.