The dual 6600GT GPUÂ’s on a single card is a good idea, but it fails in implementation.
You have to have a sli board which already comes with two 16x slots. In fact you need the board that comes with it as no one else has suitable drivers to trick the mobo into seeing two 6600gt cards instead of one.
And a single 6800GT (which costs slightly less even with a good motherboard in the price tag) out performs it.