Dual monitors w/ 4700c form factor

I am trying to run two monitors on a dimension 4700. I have installed another video card (low profile) into the PCI bus in my form factor dell. I plugged my monitor into the new card video port. When I plug in the second monitor to the original onboard video card, it gives me an error that says "unsupported video configuration detected" and "system halted!" it then tells me to plug the monitor into the add-in graphics card. Is there any way I can make this work and plug in both my monitors??? Running XP, patched sp2, Bios A04.Checked setup, but no options to change my video preferences.

Display properties, settings tab does not show second monitor capabilities. Now the monitor only works when it is plugged into the second video card, not the onboard video card.