I had XP Pro running with dual monitors for a couple of years,
switched out monitors from time to time and no problem. I've got an
Intel 2.8 MB with onboard video connected to one monitor, and an ATI
Rage Pro to the other monitor. Worked great till I had to replace the
hard drive and reinstall XP Pro. I'm running SP3 with all updates.

Now what happens is, whichever video adapter I make primary in the
BIOS, XP comes up on it, with the drivers okay, and the non-primary
one XP detects but Device Manager says the driver isn't installed.
And nothing I can do will make it accept the driver for the non-
primary one. But if I reboot and change the primary video adapter,
then it comes up with the other adapter & monitor just great and the
FIRST one is now failing to start.

When I go to Settings on Display Properties, I only see one monitor in
either case.

I've tried taking out the ATI and starting without it, then and
putting it back and restarting, no change. I don't know why this
install of XP will only accept the primary video adapter and not a
second one.