We've created two chat rooms: uci, and ccif
You can also use any number of XMPP / Jabber clients such as Adium or
Pidgin (Look for Join Group Chat)
If you are looking for a simple web based jabber client, please see
http://www.meebo.com/ and login with your gtalk or jabber.org
Once logged in you will see a start or join group a chat in the top
right hand part of your screen,
Also, these links may make it easier to join the groups
I have been able to get in with the MacOS iChat application.
From the file menu, select "Go to Chat Room..."
In the dialog box that comes up, select a jabber account
and put firstname.lastname@example.org in the Room name.
Click the "+" box if you want to add it to the list and click Autojoin to start each time
Click Go, and you're in.