I did it with just 1 GTX 570.
You have to understand 3D TV's to understand this tho.
3D TV's display 2 images to the screen (1 for right eye and 1 for left)
these images are essentially displayed at the same time.
To do this, system resources are split in 2 to accommodate.
therefore, on a 1080p display with 120hz refresh rate, each eye will only see a 720p image at 60hz
these requirements are difficult for a video card. my GTX570 did it on my Visio 1080p and 120hz. however, the resolution was VERY low for a PC display, to be able to do 3D.
HOWEVER!!!!!! Battlefield 3 looked AMAZING!!!!!! It was so amazing that I was just looking at the incredible graphics instead of playing the game. lol. killed my K/D. lmao.
Also, realize that in 3D gaming, you are seeing a left and a right view, so if you are trying to snipe or do any precision stuff, you are going to have a tough time, as there is no center image, only a left and right one...
ps. Black Ops is pretty cool in 3D from my PS3 too. Zombies... nuf said. lol.