Do you mean another 7900 GT but made by a different person like Asus or somthing?
Or do you mean a whole different modle of card?
Cards from two separate retail companies will work together in SLI mode, but they must be the same GPU model (e.g. G70, G73, G80, etc). The cards may have different BIOS revisions, different default clock speeds, or even different memory sizes. However, the fastest card - or the card with more memory - will run at the speed of the slower card or disable its additional memory
Kent.