Quote - MikeJ: it's the nVidia/ATI drivers that need to be updated for multiple monitor use. That's sometihng MS can do nothing about.

SLI can't be achieved in windowed apps, period. Maybe one GPU of an SLI tandem can be used, but neither video memory nor graphics processing can be used consecutively by two video cards in one windowed app.

SLI has nothing to do with multiple monitor usage in applications.
Although it is true it's not MS's fault. The Nvidia hardware actually has within it the capabilities, but the drivers are verbotten. ;-)