Video playback via computer

Hello! I'm a new user of the arduino system, but I have good knowledge in electronics and programming.

But cause I'm new to the arduino, I make it simle to ask you "old users" for some ideas!

My problem:
I want to make a video system in many dimensions - 3D movie, sound, vibrations, light effects and smoke.

My idea:
I will connect a computer (PC with linux) to a video projector and to a (one or more) Arduino. When giving the Arduino some kind of input (ex a start button) it will tell the computer to play the movie on the big screen. At the same time it will switch some relays to turn of lights, and start different effects.

My question:
How do I easiest implement the Arduino with the computer to start the movie? Do anyone out there know about some kind of media player for Linux as you can trig via Arduino to play/stop/switch movies, and maybe send some kind of time code back to the arduino so it can trig the effects?

How do I easiest implement the Arduino with the computer to start the movie?

How would you start the movies without the Arduino telling the PC that it needs to happen?

If there is some application you run to do that, you can make a new application to listen to the serial port, and when it gets data from an Arduino that says "It's showtime", then execute the application that actually plays the movie.