1) No, a dual chip vga card does it's work internally. As far as I know, no special motherboard is necessary.
2) The GTX2xx cards are specified as 10.5" long. Actually, I measure mine as a bit closer to 10.25" It would be good to test things out first if you can.
Cards like the GTS 250 are smaller, and some of the newer ati cards are <10" also.