Video file format of the movie and Nexus 7 is practically the same (MP4). If the movie is DRM free, you can just copy the file to somewhere else on the hard disk and the move it on the Nexus 7 storage and use the built-in media player to play the file.
If you still encounter problems, please download an appropriate video converter which will help you convert the same file but with Nexus 7 support.