Most, if not all, motherboards with onboard video disable the onboard
video when an AGP card is present. The AGP bus was designed for only
one card, and the onboard video uses that bus when no card is present.
You can slap in an extra PCI video card to do dual display, though.
I've yet to hear of an onboard video card that supports dual monitors,
but any recent Nvidia card and most recent ATI cards do support it
(anything in the last two generations, at least, of Nvidia support dual
DVI, though not all manufacturers equip both outputs with DVI ports.
DVI+VGA has been supported since the Geforce 1, I believe). Never tried
to enable it in linux, though, so I'm no help there.
Greg
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