Hmm
I run XP Pro and Dual monitors, yet my PCI card is in the 3rd slot, and I have it on Initialize AGP first..works flawless for me. Actually I thought you had to keep the PCI Video card out of the first slot because it usually shares an IRQ with the AGP card, which shouldnt, but might cause conflicts.
ITs a Geforce2 GTS AGP with a Matrox Millenium PCI.
A bonus if you have at least one Nvidia card - You can use the Nview extensions, which allow you to have virtual desktops, transparencies when dragging, and special rules for popups (appear on first screen always, or appear on screen of app, or appear on screen where mouse is) and other stuff like that.