Down the bowels, and beyond!

Download mumble:
http://mumble.sourceforge.net/ (you want 1.2.0 Stable for Windows)

Don't skip the audio wizard at the start - it's short and the end result is your mic sounding great in everything, not just Mumble.

Connect to server > Add New...
Servername: Con Fiddly
Address: 118.127.0.235
Port: 21015
Username: whatever you like