In IM+ Lite, choose More at the bottom of the screen. Choose Accounts and then Edit. Hit the 'plus sign' (+) in the upper left of the screen to add a new account.
When it prompts you to "Select a service," choose Jabber.
It will then ask for your Login, your password, and your host. Your Login is your SIP address, firstname.lastname@example.org and your password is your WWW password. The application will automatically fill in the host field.
If you have problems connecting, re-check your password. You can also try setting the Host to "xmpp-client.onsip.com" and keep port 5222.