Ventrillo works pretty well or used to I haven't had a need to use it for nearly a year.
There is a setup guide online that I followed.
http://www.ventrilo.com/tutorial.php
There are others online but the one above is pretty clear.
http://www.multiplaygameservers.com/...entrilo-guide/
http://www.ventrilo.com/setup.php
Essentially one person needs the server program and the client that person sets up the server on his computer and allows the others who use his IP address and password to access the server.
Note you need to run the client program and join your own server.
We used it in team games rather than Skype because we could set up several channels.
We all began on channel 1 Base then each team left to go to red and blue channels so teams couldn't overhear the other team.
Worked very well for our group.