First thing's first, go get Mumble and set it up. Once it's installed and you've configured your mic, come pay attention to this.
On the Mumble Server Connect screen, click the add new button.
Go ahead and label the server what you will, but make sure the address is panda-games.mumble.com and the port is 3126. Go ahead and use whatever you will for a username, I put in mine as an example
Now select the server and hit connect! You will be prompted for a password, in which case the password is pandas_rule