How to Use IRC
Downloading a client
To join Applefritter IRC, first download a client. A few Mac OS X clients to choose from are:
Colloquy
Ircle
Snak
X-Chat Aqua
IRC software for other platforms:
Mac OS Classic: ShadowIRC
Newton: ChatBuddy
Apple IIgs: Samurai IRC
BeOS PPC: Birch
BeOS Intel: Felix
Linux: xchat
Amiga: AmIRC
Atari ST: AtarIRC
PalmOS: PalmIRC
EPOC: nICQ
OS/2: EZ IRC
Windows: mIRC
Connecting to Rizon
Now that you've installed your IRC client, you need to connect to a Rizon IRC server. A complete list of servers is available here. A web interface is also available.
The recommended server is irc.rizon.net, port 7000. Enter this information into your irc client, along with your desired nickname. Connect.
Once the client has connected, type "/join #applefritter" in the input box to enter the channel.
For more information, see the Internet Relay Chat Help Archive.

Xchat
They also have Xchat binaries for windows.