Reading back my own posts in this thread I need to add that I ended up returning the TH2G device from Matrox because the distortion caused by TH2G was unbearable since it assumes all connected monitors are aligned in the same plane. Instead use two 8800GTS 512 MB cards. This gives me 4 accelerated heads.
However, they can not work as a single monitor in the same way as the TH2G can.
So I further developed my graphics engine and added "Virtual Windows". This feature allows me to place any number of screens at any location and orientation. The engine will ensure that the perspective as seen from the users point of view will be such that all screens appear to act like window panes onto the same 3D world.
Optional a head-tracking device will even allow the observer to move their head thus enabling them to really "look around the corner"
I made this demo video to show what I mean: