well, you can go anything from a DMX to keyboard interface to a catalyst (was replaced by Axon, though there are tons of catalyst out there) to what john mentioned or the arkaos
Keep in mind the catalyst eats up an entire universe, so that might be something to consider.
Funny that this came up today. I just went to a High End Systems demo yesterday. Got to see the Road Hog, Showgun, and DL2. Pretty impressive. So, there is the DL2 that you could use for video playback. I believe that PRG is still making the MBOX which is a media server they designed, that can be controlled over DMX, supports HD content and is capable of driving more than one projector.