Its not really that hard, add a point_clientcommand into your map and name it 'blah'. Then when the player walks into a trigger make the output: ontrigger, (the name of the point_clientcommand), command, playvideo <your.bikname>.
(Make sure your .bik file is in the media folder!!!)
I believe this only works in ep2 though as the other games dont have the playvideo cvar.
Good luck.
