Wow, thanks for all the replies! Since there's so much interest, I'll cover the project in more detail.

We're combining bluescreened video of actors with synthetic backgrounds. This video is being rear-projected behind live stage actors. We've overcome a lot of the technical issues, but 1024x768 isn't enough resolution to make any video look reasonable when your actors are life-size on a ten foot tall screen, especially since the useable resolution would be closer to 1024x512, after fitting the projection to the size of the screen.

So to answer the questions about the rig, I know it has the raw HP to crank this video out. It's a 7200 RPM drive, but if I needed to, I could pull a 5-drive 15,000 RPM SCSI RAID 5 array out of my server. I think I'll save that for when I'm doing movies! The video card is from Siluro, and uses the GeForce 4 Ti4200 chipset. The board is standard reference design and is cooled enough to overclock well if I need it to. It supports dual monitors through an analog and DVI output. I already span my desktop across both monitors with much success. It does have s-video TV out, which can be used simultaneously with either one (but not both) of the other outputs, but I'd much rather use the analog and DVI outputs to keep the resolution higher. I'm using the drivers from NVidia, but I've tried the ones from Siluro and they appear to be the same drivers rebranded (as I would expect).

My problem is much like patweb said. Windows has no problem supporting many monitors, but it only wants to support one monitor powerful enough to display any video or 3d on.
Maximum PC in their latest (1/2003) mag says,

"Some NVidia boards will let you stretch a 3D game across two monitors if you use the stretch mode setting instead of setting independent resolutions and refresh rates for your two monitors. In order for this to work, your game must recognize the odd refresh rate that it will have to run."

I take this to mean that it might be possible to get my rig to work if I use a different driver set and find a compatible piece of software. Maybe someone out there has already done it.

Thanks for all the feedback so far. I'm hoping I'll figure this out without having to install another OS. Any ideas are welcomed.