I know you can have two graphics card at same time Crossfire and SLI, but is there a motherbard that can support more than just two say three or even four cards. I heard something about it but do not remember. There something about having the option of having four cards all running in SLI with all 4 PCI-X slots running at 16x each. I think the striker has three PCI-X slots but one is running at 8X not 16X speed.
PCI-X is NOT PCI-e. Google it!. You can get graphics cards that have two GPUs on one card. This lets you run SLI on a non-SLI motherboard. If you have an SLI motherboard, you can run two of these cards and get QUAD SLI. This is mainly for use with very high resolution displsy, usually large LCD. 2 GPU does not give double performance of 1, and 4 GPU will not give anywhere near 4x performance.
There are a bunch of 3 and 4 PEG 16X slot MoBos out there, the first being intel and tyan with 4X slots, then gigabyte 8X slots, and then many more followed. THG looked at the early Gigabyte board a long while ago (2005) caused quite a stir back then; http://www.tomshardware.com/2005/10/04/one_gigabyte_mot...
These and more recent models including the striker have been eyed for both 3-4 card SLi/Xfire as well as multi card rendering + physics.
The two connectors at the top of the X1950Pro/X1650XT, GF8800GTX, HD2900XT and HD2600 series would allow you to daisy chain more than two together.
Like Mike99 said it's PCIe or PCI-EX not PCI-X for SLi/Xfire.
And right now no chipset supports the 64 separate lanes for four 16x graphics slots, however that is supposed to change with future chipsets, and the modular design of some chipset like nV's could be made to add extra lanes, but it's expensive and ultra niche and not worth it at this time.
For now the support will be limited to combinations of 16X and 8X or even 16X/8X and even 4X. But even four 8X slots should be more than enough to get benefit from the 3rd and 4th cards.