I have a dual projector rig myself so i guess i can help with info. Additional info can be found here: viewtopic.php?f=26&t=509
As is today every projector there is works with a dual projector setup (even lcd-projectors but you MUST use polarizationangles of 45/135° with lcd's!). However i'm not sure how the newer LCoS lcd's manage until someone comes up with info. Possibilities are that they works good also.
Compability: As said you need a dual output card. Nvidia or ati doesn't matter since nvidia doesn't support anything else than their 3d-vision setup + the zalman screen. This is not obstacle since you have both iz3d as well as the tridef ignition drivers to use. The iz3d driver costs 50$ one time fee for dual outputs.I have yet to try the tridef ignition. Peter Wimmers stereoscopic player supports it greatly so everything in 3d media is playable.
Future eventual caveats about dual projector rigs: Stereobroadcasts and consolegaming (because of the need for two outputs...) will most probably not work but everything you run with the computer (and of course supported in stsreodrivers etc...) should work excellently.
Choose projector after what you need but make sure the projector has lenseshift or at least digital keystone correction. Lenseshift is best though.
Besides projectors you need a silverscreen that preserves polarization. Check info here: viewtopic.php?f=3&t=2719
If you wants to get some cheap but also good filters you can get them at polarization.com.
Linear or circular polarization? Take my word for it and go for linear polarization! If you like you can try and get circular polarizers as well but the experience with linear is more than twice as better! Virtually no ghosting or colordistortions of which you get both when using circular.
Mb: Asus P5W DH Deluxe
Cpu: C2D E6600
Gb: Nvidia 7900GT + 8800GTX
3D:100" passive projector polarized setup + 22" IZ3D