MSU:
Let me make sure I understand your setup correctly.
You have a built-in (to the motherboard) AGP dual video out? Which gives you two monitors.
You then added a PCI card to add two more monitors.
Now you are trying to add ANOTHER PCI card to add two more monitors.
For a total of 6 monitors coming out this baby?
First, I've never heard of dual built-in AGP ports. I've heard of connecting a dual card to ONE AGP port to create what you are talking about. Is that what you are talking about?
Second, any time I've installed extra cards, I had to remove all the video drivers for all of the currently-installed cards. All of them. Go into Hardware Manager/wizard and totally uninstall them. Cut the computer power. Then, install the second and third card, and reboot. Then, install software as it asks for it.
Third, what makes you think it isn't recognizing it? Just not showing up at all in your hardware manager? You very well could be causing conflicting IRQ ports and other crazy motherboard issues. In which case, you really need to do the above step and let the auto-setup do its magic. XP Pro generally does a good job of it.
Fourth, I just took some medicine for a nasty head cold and should be visiting another planet here shortly, so give me until tomorrow to reply after I hear how well this blows up your machine. <g>