Dual head/Dual Video cards in Linux "how to"

Ok linux gurus,

I have an older work machine that is a Compaq Deskpro EN series with the 733Mhz proc. Up until the other day I was running the onboard graphics adapter with a single display.

I aquired a second display and thought I would dual head the displays using any combination of the following:

Onboard AGP graphics or ATI MACH 64 in the AGP slot

Two PCI IBM/Cirrus Logic video cards.

I have tried every combination of the above cards together and I can get every card to recognize and configure individually in Linux. Using the BIOS I am able to get only one or the other card to recognize at any time (never two).

I am thinking that this is a BIOS issue, but I have never dual headed in Linux (SGI IRIX Many times).

Any tricks I should try?

Running RedHat Fedora Core 4

EDIT: PS.. I am able to go through the boot loader on one display and have it StartX on the other Display. But everytime I try to config for BOTH to start in X Xconfig fails and defaults back to a single card. This is what makes me think it is maybe POSSIBLE.