Google apps for chat allows us to chat to other google users using our own domain like firstname.lastname@example.org or email@example.com.
To do this, you have to register for google apps account using your domain name. Then login using using firstname.lastname@example.org as your user id in gtalk. Simple!
However, pidgin throws an error message if you try to create a new google talk account with you@yourdomain as the user id. Instead use the following settings,
Protocol: Google talk or XMPP
Username: your username without @yourdomain.com
Click on ‘Advanced‘ tab and enter ‘talk.google.com‘ in the Connect Server box. This does the trick!