Contrary to what has been said here, SLI does work with the demo. However, it does so very poorly. In Vista there is almost no gain at all. In XP with DX9 it is "better" but not where it should be. Nvidia has already said that SLI improvements were needed in the game and in the driver.
The only combination that SLI works decently with in my own experience is with XP in DX9 with the 169.01 betas. Running that combo I can average about 45fps in SLI and 25fps with a single GTS card.
As for Vista and SLI...I'd forget about seeing any meanignful gains until the drivers and game code are reworked.
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