Try google? sigh.
The first match on
http://www.google.com/search?q=jabber clearly explains what Jabber is-- in fact, the very next match is conveniently titled "What Is Jabber?"
Anyway, to the OP:
Google would probably help you as well, more than we can anyway:
http://www.google.com/search?q=jabber+mircOtherwise try
www.mirc.net or
www.mircscripts.org, but I don't think I've ever seen one personally.