Google Talk officially announced on January, 2006 open federation with other Jabber servers. This allows users of any other Jabber server to chat with Google Talk users.
The only requirements for this is support for Dialback and DNS SRV. ejabberd includes support for the first requirement and Erlang/OTP includes support for the second. Erlang R10B-x has a bug that prevents the correct behaviour of DNS SRV.
If your Jabber server can't connect with Google Talk, please check this page: Fix DNS SRV bug.