you don't need SLI if all you are doing is playing WoW, its pretty much a waste. I run a c2duo 2.4ghz with a 8800GT hooked up to a 47" LCD and two 21" LCDs (flipped sideways) and it runs 5 copies of WoW fine. Your 8gb, vista, quad-core PC will run it even better! My 3d monitor is hooked up to my onboard VGA controller with 8mb of memory (LOL!) and I don't notice anything different about it. WoW is not a graphics-card intensive game, CPU, computer memory and hard drives are the gating factors for WoW.

I'd suggest either a cheap 8800GT now and upgrade to a new top of the line video card in a few weeks, or go ahead and buy a nice top of the line NVidia or ATI (260/280 or 4850-4870? not sure about model numbers). The former will net you probably 20fps main and 10fps alts, and the latter will give you 40fps main and 20-30fps alts.

And yeah WoW on a main screen giant LCD is awesome. I run mine windowed mode at 1600x1200 and its fabulous. I rarely even look at the alt windows, they are just there in case I need to loot or rez.