If gtalk is not listed in the gaim protocol field there is an easy way to add google talk to gaim.
Select the Account menu > select Add
Choose Jabber as protocol
Enter your username at the screen name. You need not enter @gmail.com. If your email address is firstname.lastname@example.org then you have enter abc.
Enter gmail.com at Server field
Resource field can be left empty or you can type anything you want. This field is unnecessary for our purpose
Enter your password
In the advanced tab
Leave Force old SSL" and Allow plaintext auth over unencrypted streams unchecked
Port should be set to 5222
Enter talk.google.com at Connect server field
Save this new account.