I'm in the process of trying to set up a dual card, triple head nVidia based system on Karmic Koala.
So, after being unable to get a 7600GT and 9800GT to play nice together when Xinerama is enabled, I borrowed a 9600GT to go into the mix. Now I can get three screens in one single desktop, but....
When Xinerama is active, compositing goes away.
There's been a bit of discussion about this, but not anything in the way of a good solution. I'm wondering if the problem is with the nVidia drivers, (I'm using 190.42), or with Xorg itself.
Until ATI's drivers settle down, and I get my hands on an Eyefinity card, I'm stuck with the nVidia cards. On one card, with dual-head, nVidia is awesome, and the best solution available, but when you introduce a second card, things seem to turn to sh_t.
So, after testing the setup in Vista, just to QA the hardware, I'm now back to trying to coax Linux into giving me what I want. I've been lead to believe that I can have a dual card, composited desktop if I install xserver-xgl (which doesn't seem to be in the stock repos), but it supposedly produces sub-optimal results.
Anyone out there with a triple head system in a satisfactory way? Any help would be gratefully recieved.