Are the 8800GTS pci cards?
No, they're both PCI-Express 16x cards. There are a bunch of motherboards available with 2 x16 slots, and a few high-end boards with 3.
If you have two of the same size monitor, you could just use one 8800GTX/Ultra to run both in span view mode. One of those should handle 1680x1050 x2 without too much trouble. Since I'm using just 1 8800GTX on a 24" 1920x1200 and a 20" 1680x1050 in the worse 'dual view' mode, I'm seeing a framerate hit on the 4 alts on the 20" (/console maxfps 10). However, my main running 1680x1050 windowed mode on the 24" monitor is still very playable. If I had two 24" monitors, I'd just use the span mode and all 5 WoW windows would probably be much smoother. I still haven't attempted a crowded battleground yet - so we'll see when the time comes if I'll need to upgrade.