Also look at the first three links on this page
http://www.ralphjohnsuk.dsl.pipex.com/page5.html
The first tells you how to set upop a Jabber screen name to use the Jabber side of iChat.
The next tells you how to arrange what aree called Transports to connect to other services like MSN.
The third link is need before you commence the stuff in links one and two as it is a list of the Jabber servers and their Capabilities which are needed to identify which servers have which transports.
Having said all of that this only allows you to
Text chat to these other services/Buddies this way.
Rj's list of other MSN compatible apps seems the way to go for Video and Audio chats.
8:59 PM Sunday; October 8, 2006