Can't connect to GTalk

I think I'm suffering from the use of my own domain and Google Apps, instead of just standard gmail.

When I enter the email I use for Google Talk, twitter pretends that everything's fine, but nothing shows up on the other side.

If I try to enter twitter@twitter.com as a contact, the client insists on sending an invitation to chat, which doesn't include the six digit jipjap (or similar) code and so (I assume) is just ignored....

Please help. I just want to use the service.