Someone I used to know wrote a large chunk of icecast, which is an open source alternative to shoutcast. I would think your best bet for synchronising them is to make sure all your clients have exactly the same settings... Manualy set the connection speed and buffer size, and don't let it automaticaly pick something else. There was a good article on slashdot about Disney doing the same thing at one of their new theme parks, but I suspect their solution might be overkill. (might have been Wired magazine, or both...)

Matthew