Jabber is a XML based instant messaging protocol. It's different from AIM in that it will store messages left for you while you are not on for you on the server and deliver them for you when you log in. We have a Jabber server set up at danm.ucsc.edu.
Your jabber username is your username @danm.ucsc.edu
What follows is a list of how to configure various chat clients to use this service.
(a great aim client for os x,
link)
Security: check the following: