Cathnet members use irc to chat with each other. IRC stands for Internet Relay Chat. It is much like msn, yahoo chat, and is primarily used by developers or people who want a simple chat application.

Plone uses irc as it's primary chat tool http://plone.org/support/chat.
Cathnet uses irc to chat with each other. our channel is  irc://freenode/cathnet

The easiest way to connect is to use the firefox extension chatzilla. Here is how to do it.
1) If you don't already have firefox loaded on your computer, then download from http://www.mozilla.com/en-US/firefox/ and install
2) With firefox open click on Tools>Extensions>get More Extensions(bottom left) this will take you to the extensions page.
3) scroll down to the search box and type in chatzilla and press enter.
4) choose chatzilla and install. Once installed you will need to restart firefox by closing all firefox windows and dialogs and then starting firefox again.
5) click on Tools>chatzilla. This will open up chatzilla. Then on the welcome screen you will see freenode underlined. click on it. This will open freenode. Once it has stopped opening, click on IRC>open channel and type in cathnet and click join. You don't need to wait for all the channels to be listed.
6) once you have joined cathnet click on IRC>Open this channel at startup. Next time you just have to open chatzilla and cathnet will automatically be opened.
7) other channels that you might like to join are zope-au, plone and zope.
8) welcome to the club :)