MultiScreener looks very handy if you need to play movies on multiple screens and want to keep them sync'ed up... MultiScreener is a set of freeware applications that synchronize the playback of Quicktime movies on multiple computers, using a local network to tie them all together.
It is intended for multi-screen video walls, multichannel art installations, and the like. (It's an alternative to Pioneer DVD Players and expensive synchronizer hardware.) There are two applications: Server and Client. The server plays a movie and sends position information over the network. Each client compares its position to the server's and changes its playback speed to compensate.
http://blog.makezine.com/archive/2008/04/multiscreener.html