I think you need to activate your chat account with another client first, for example pidgin.  Here are the instructions from Facebook:

   1.
          * Start your instant message program and locate the menu where you can add a new account (usually in preferences or settings).
   2.
          * Create a new account by entering the following info:
          * Protocol: XMPP or Jabber
          *
            Username: quinn.plattel
          * Domain: chat.facebook.com
          * Jabber ID: quinn.plattel@chat.facebook.com
          * Password: <your Facebook password>
   3.
          * Enter the following server info, as requested:
          * Port: 5222
          * Server: chat.facebook.com
          * Use SSL/TLS: no
          * Allow Plaintext Authentication: no

qiet72