I've been struggling with this for several days now, and I'm ready to go back to Windows if I can't get a workable solution.
I recently loaded a Dell desktop with Wheezy with the onboard AGP, a 3Dfx voodoo3 card and a Diamond Stealth 2000 pro. All three video interfaces are reconized, but the monitors are not and only one monitor has a desktop displayed. The other monitor is just a blank screen.
Just to prove a point, last night I loaded Wheezy onto an old MMX machine using the same video cards and monitors. Sure enough, only one video channel works.
Any help would be appreciated.