Hi
I have older Shuttle Boxen with NVidia chipsets and got several projects done with it so far, in Windows and Linux. With the proper drivers installed, the chip accellerates 2D/ 3D operations so an additional card would not gain you so much in this case, I guess. Actually I bought the Shuttles for exhibitions because they came with all built in for a low price and so far my framerates are fine.
Cheers,
Malte Steiner media art + development -www.block4.com-