I have a gateway machine with a onboard video card (NVDIA GeForce 6100).
I also had a GeForce FX 5200 PCI dual monitor.
The BIOS has an option for INIT display.
When started, the primary display is the onboard card.
Then, the dual display FX 5200 takes over and the onboard card shows has "This device cannot start. (Code 10)". So that I cannot use the third monitor.