Since installing XP I was unable to get second monitor to work, could not find drivers for my PCI card for XP, was getting that yellow question mark besides my second display driver PCI. Finally played around in the BIOS in INTEGRATED PERIPHERIALS on tyan s1854 (wording could be different on other motherboards), changed the setting INITIAL DISPLAY FIRST from AGP to PCI, the opposite of win98 and ME, rebooted and all is fine. XP used a driver, now boots on PCI then goes to AGP and both video cards are recognized.
Hope this may help someone with the same problem