supersloshy writes "Facebook Chat has so far only been meant to be used in a web browser, and instant messaging applications have had a hard time implementing its undocumented protocol. Today, Facebook is making this job much easier by enabling support for XMPP to access its chat service. AOL's AIM and the Empathy Instant Messenger are also including pre-set Facebook options, due to already supporting XMPP."
Here are instructions for setting up XMPP Facebook chat
with popular instant messaging clients, including Pidgin and Adium.