Intel Extreme onboard integrated graphics: can be used wit..

My question pertains to a Soyo motherboard (SY-P4I845PE/GVISA Plus)
with Intel 845PE/GV chipset. I believe this chipset has an integrated
video controller with 8 mb of video memory (this component seems to be
called "Intel Extreme Graphics").

I belive that my question may very well pertain to any motherboard
with an Intel Extreme Graphics component that is part of the
motherboard.

My question is this: Is it possible for the Intel Extreme graphics
adapter to be functional under Windows XP in addition to a PCI-mounted
video card?

I say PCI because the Soyo motherboard in this case does not have an
AGP slot (and it doesn't have PCI-express either).

For example, I recently installed an ATI Radeon 9250 PCI video card
into the above Soyo motherboard and tried to get the on-board Intel
adapter to function, but it simply wouldn't drive a monitor when the
ATI was active. The ATI board has dual monitor support, and when
bringing up the configuration window it appeared to know that there
was a third monitor available to it (which would have been the
on-board Intel Extreme) - but it wouldn't let me set the display
resolution (it was fixed at something like -1 x -1 instead of the
typical 640 x 480, etc).

So my experience so far is that given a motherboard with an integrated
Intel Extreme graphics adapter, that adapter can't function as a
secondary display adapter when another adapter is plugged into a PCI
slot. Is this true?

PS: The Soyo wouldn't boot unless I had the ATI Radeon card plugged
into the second PCI slot. When plugged into the first PCI slot, the
machine wouldn't even post. What's up with that?