this tutorial will show you how to set up a multi-head system in most linux distros, primarily ubuntu. please note, this is still largely unfinished.
Step 1: Install your hardware.
the title explains it. i'm assuming you know how to open the case and install the cards. just make a note of which card is where and which monitor is on which card. FYI: my system uses one Nvidia riva tnt2, one nvidia riva tnt, and one 3dfx voodoo3. (in that order on the pci bus)
Step 2: Boot up and get x going
if X fails and drops to the terminal type in:
sudo dpkg-reconfigure -phigh xserver-xorg
(if you're already root, don't use sudo)
use the wizard to set up drivers for whatever monitor the wizard is showing up on. (usually the first on the bus)
reboot to start x
Step 3: Check the order and find the addresses
by now you should be looking at your linux desktop on one boring screen.
open a terminal and type
you should now see a list of devices and their bus id. find the graphics cards and write down the bus id's you'll need them later.