Add a texture to the plane (duh), in the texture buttons, (F6), select Image and select Movie in the image box.(Interpol, mipmap and movie should all be selected). Then select Load Image and find your movie. It must be an .avi… and some .avi’s won’t work but most mine do. If your’s doesn’t, you’ll need to re-encode it.
Then in the Anim and Movie box, set the number of frames the movie has, use Offset to start wherever you want, and lastly set the StartF to set what frame in the animation you want the movie to start playing, and the length to say for how long.