switching between video with a motion sensor?

I have an upcoming project where i need a motion sensor to change a video projection from a black screen to another video. I am wondering what the best approach would be. The project will be running for 2 weeks for 12 hours a day, so I would prefer not to use my laptop. would it be complicated (or possible) to get a dvd player to change chapters with arduino? any suggestions would be much appreciated! thanks!

oh, i'm really new to the software. and the hardware.

You could maybe look at some of the infra-red remote applications - go over to the Playground and look around. Sounds feasible to me.