Hm.. I dont know Jabber, is it a centralised system?
Implementing chatsystems in decentralised networks is quite hard because its hard to syncronise all messages.
Few clients already support a *chat*, but only a chat where two users can participate, plus you have to know the IP of the other user...

Building in IM services is hard to because many users have
dynamic IPs so you cant check if they are online since they dont log in on a central server.