Never heard of any software for that, but if it exists, it'd be pricey, and might require special hardware decoders I reckon.
TV signals ain't in the right format to broadcast over a LAN, so it'd have to be decoded, recoded in a LAN - friendly format, then sent and decoded at each LAN station. Would need really fast PC's for that, too. And wouldn't be exact real time, either, as you'd get lag from all the decoding etc.
I could be wrong, though, as I dunno that much about video feeds.
Cheers
Mick