http://mumble.sourceforge.net/
INFO
1. download mumble (stable recomended)
2. Install
3. Follow wizard for setting up your audio
4. Server -> Connect
5. In the server list, click "add new..." and put in the info below
Label: PT23 Mumble Server (what ever you want, its your label of the server)
Address: pt23.net
Port: 64738 (default port)
Username: bob (Your user name in the server...please dont use bob? lol =D )
For example!!