Here’s how to get on to the Google Talk or Google Chat service on your custom Google Apps domain using Pidgin.
Assuming your username is john.doe and your custom Google Apps domain is example.com.
- In Pidgin, Accounts -> Manage Accounts -> Add
- Under the Basics tab
Protocol: XMPP
Username: john.doe
Domain: example.com
Resource: <blank>
Password: <your password> - Under the Advanced tab
Require SSL / TLS: Check
Connect server: talk.google.com
(Leave everything else to default settings) - Click on Add, and connect away!
For a guide complete with screenshots, go here.