Hold'em tourney software

[cavalier]

Does anyone know of software that I can use on a closed network to host a Hold'em tourney?

Specifically, about 5 of us work behind a firewall and want to play Hold'em tourneys at lunch. Because of the firewall and site filters, we can't get to lots of places on the internet having to do with gambling.

We hope to find software that will let us play without needing internet connections.

Ideas?