Google to the rescue :
Kopete handbook
Gaim is also very popular for instant messaging, so check it out
Gaim is a multi-protocol instant messaging (IM) client for Linux, BSD, MacOS X, and Windows.
It is compatible with
AIM and
ICQ (Oscar protocol),
MSN Messenger, Yahoo!, IRC, Jabber, Gadu-Gadu, SILC, GroupWise Messenger, and Zephyr networks.