In W2k, I noticed that if/when you decide to remove the second monitor after trying this, you must do so via the "Expand desktop" pickbox first ... otherwise you will likely experience driver problems, as I did, with the initial vid card. The system would boot with the default VGA driver and not recognize my vid card. An easy fix, when I just put the second card back in, rebooted the system and then unchecked the "Expand desktop" pickbox.
Confused? Well I was, until I figured this out.
c:::HNsaw