It's the GeForce 7900 GTX Duo, a graphics card with two 7900 GTX GPUs.
Normal Quad SLIs have four different graphic cards, especially designed by Nvidia. This new SLI will let you plug two new cards, each with two GPUs in your Nforce 4 SLI motherboard and it should work.
Those cards will need a lot of power but it will be cool to read a review of such a powerful system. This is definitely going to be a price and performance Bugatti but if you have a million dollar house you can get Quad SLI as well.