Dual Monitor Disable (in XP)

I have a Dell Dimension L866R with onboard video, I recently acquired an Nvidia Ge-Force 2 MX400/400 PCI and I am trying to figure out how to disable onboard video. Either the onboard works or the card works but when one does I have to switch to the other to see my Log In screen. I have tried switching from On Board to PCI in the BIOS, this only causes me to have to remove the CMOS battery to get the on board video to work again. Currently windows (XP Pro Edition) is trying to use both video outputs to do dual monitors. But all I want is for my Ge-Force, to work, I don't want to have dual monitors. So any help in disabling the dual monitor feature would be greatly appreciated. Thanx in advance. :)

Is there possibly a place in the bios to allocate memory ot the onboard where it may be set to none disabling it?
Also it could be a jumper on the mainboard itself

Yeah, some of those Dell's can be a beatch.
Usually, with the newer ones, just puting the new card in should disable the onboard video. If that is a glitch with your board, perhaps you can try to just disable it: the onboard video, in Device Manager.