I am wondering if it's possible to have an Arduino interface with a GPU using any of those above mentioned interfaces, as long as I know what the GPU is.
It would be an older GPU like an ATI Rage of some kind with a PCI interface.
Do you think that would be possible at all? I'll probably need a 12v output too, the ATI Rage doesn't require a lot of wattage either, its' a lowprofile card from 1997 or so.
Possible?
Maybe.
Desirable or sensible?
Almost certainly not.
Well, I'm trying to find a GPU to produce images via VGA instead of using the internal clock of the arduino to produce an VGA RGB image. If not via the PCI/AGP/PCI-e interfaces, have there been any attempts to wire up a GPU with the Arduino?
There are companies that produce smartgpu's that you can hook up a microprocessor to. One that I bookmarked, but never have bought from is Vizic technologies with their smartgpu, minigpu, etc. products. I'm sure there are other similar companies: http://www.vizictechnologies.com/
However, it may be better to step back and describe what you are trying to, and explain why you are trying to do something on an Arduino? An Arduino is likely not the best solution, due to the Arduino being slow and having limited memory.
I would think a better approach might be having a processor that is faster and has more memory (possibly having one or more GPUs as well) doing the higher level functions, and use the Arduino where it is best at (handling sensors/motors/etc. in real-time).
Something like a Beagle Bone Black, Rasberry Pi, PcDunio to drive the visual aspects, hooked up to an Arduino via usb, bluetooth, etc. Or maybe this might be something Intel Galileo would be good at (it has to be good at something), or the Yun (assuming you can find one), or the Tre (when it starts shipping next year).