Setting up a Google Talk account
To set up a Google Talk account you need an existing Google Mail (GMail) ID which at the time of writing are only being offered by means of invite.
How do I set up a Google Talk account?
Create a new account as if you were creating a Jabber account, using your full GMail address as the Jabber ID. Navigate to the Account Options tab and set the host name to talk.google.com and the port to 5222. Click OK to finish.