Okay, completely on accident I managed to get the binary opengl
supporting nvidia drivers to work with xinerama. A clean reboot was
probably the key. ;P

http://www.haxxed.com/random/openglmultihead.jpg

HELL FREAKIN YEAH!

Screenshot swappage killed the framerate, I get about 30fps at that
point in the level, and ~50fps everywhere else, with a TNT2 Ultra in a
1024x768 window in 32bit color. The right screen is a TNT1 run by the
stock nv driver, and the left screen is a 3dfx banshee.

And the textures are gone because its competition settings. ;)