Cannot get 3 monitors to play nice [Ubuntu]

[Mark]

Using 3 monitors. Funny problem.

I am running Ubuntu 10.04 and my current setup is;

Motherboard: Asus P5Q Deluxe
Card 1: 8800GTX
Card 2: 8400GS
Monitor(s): 3x 22"

The problem i have is that i can get the two on the 8800GTX to work together but i can only get the one on the 8400GS to work as a "Separate x screen" which is no good because i can't drag windows or anything over to it.

I've tried editing the /etc/X11/xorg.conf file but i don't *really* know what to change and i have no idea why the 8400GS will ONLY go as a separate.

Any ideas?
Thank you.