The secondary monitor shouldn't show anything before the login screen appears, it should stay black.
The display initialization sequence should be agp first.
When xp loads, it finds the secondary display adapter and monitor, installs the drivers and it's ready. You only need to expand the desktop to the other monitor then.
I have a gf2mx400 as my primary adapter hooked on 21" compaq and some elsa gloria synergy as secondary adapter hooked on 17" nokia, works fine.
Back when running w2k I had some cirrus logic adapter, but xp refused to function with it so I had to change.
Initializing the pci adapter first makes it the primary display and that is not what you want.
-M