Nvidia 94.43 (i think) Beta Drivers do this. They have to be the same type of card however. You can't mix a 7900/7800 or 512/256. A BFG 7900gt 256mb and XfX 7900GT 256mb would run together with the new drivers. But....crossfire will run any set of cards together backward to the slowest card.
Noli Nothis Permittere Te Terere!!
EVGA 680i, Dual EVGA 8800GT'S (650/950), 4 gigs OCZ DDR2 1066, Intel Q9450 at 3.8 Ghz, Koolance Water Cooled, Dual Plextor16x DL DVD+/-RW. Dual WD 250gb 16mb Cache Sata 3.0. 3DMark06 score = 19,168.