I want to be able to sync video players on multiple networked machines. Ideally I'd pre-send video files to each machine and then one of the machines would spew out some kind of timecode to get everybody playing together.

How close to frame-accurate could I get? I there a way to do SMPTE over ethernet? I can't find anything. Is there a better, non-legacy time protocol to use?

Any reading material or somewhat related projects you could point me to would be greatly appreciated. So far I've been looking into gstreamer, xjadeo, (would JACK help?)... If I could get VLC or mplayer to do this easily, that'd be sweet.

On a small network, using UDP, you could get very low latencies... well within what would be necessary for video synchronisation, I would think.
The issue would not the networking side of things though, but the video player end. Do you know of a video player that will do a master/slave configuration such as you are describing? If so, how does it transmit/recieve the timecode currently? Almost all internal communication in Linux is via sockets or named pipes, and these could be co-opted to send your timecode through the network instead of locally.

So far I've found out that that xjadeo project somehow syncs video to audio (for making soundtracks) through JACK.

I wonder if I could just update once in a while, and have the players free-wheel in between updates.