First, you need to have the nvidia driver installed if you don't, please install.
In a veague rememebrance. It went somethign like:
Connect up Monitor 1.
Use 'sudo nvidia-settings' to 'save to x configuration file' and save it in your home for reference as ~/xorg1.conf
Shutdown. Connect Monitor 2 to Port 2. Bootup.
Use 'sudo nvidia-settings' to 'save as' the configuration. and save it xorg2.conf
Shutdown. Connect Monitor 3 to Port 3. Bootup.
Use 'sudo nvidia-settings' to 'save as' the configuration. and save it xorg3.conf
Manually Combine the information for each of ~/xorg files.
backup a working copy of the /etc/X11/xorg.conf
save the super modified xorg file as /etc/X11/xorg.conf
You also might get luck with using nvidia-settings with all three montors after you correctly configure them. In my experiance from Xorg (was actually xfree86? then), is a picky creature and manually editing is hard.