Добавляем в зону следующие DNS-записи:
_xmpp-client._tcp IN SRV 20 0 5222 talk1.l.google.com.
_xmpp-client._tcp IN SRV 20 0 5222 talk2.l.google.com.
_xmpp-client._tcp IN SRV 20 0 5222 talk3.l.google.com.
_xmpp-client._tcp IN SRV 20 0 5222 talk4.l.google.com.
_xmpp-client._tcp IN SRV 5 0 5222 talk.l.google.com.
_xmpp-server._tcp IN SRV 5 0 5269 xmpp-server.l.google.com.
_xmpp-server._tcp IN SRV 20 0 5269 xmpp-server1.l.google.com.
_xmpp-server._tcp IN SRV 20 0 5269 xmpp-server2.l.google.com.
_xmpp-server._tcp IN SRV 20 0 5269 xmpp-server3.l.google.com.
_xmpp-server._tcp IN SRV 20 0 5269 xmpp-server4.l.google.com.
_jabber._tcp IN SRV 5 0 5269 xmpp-server.l.google.com.
_jabber._tcp IN SRV 20 0 5269 xmpp-server1.l.google.com.
_jabber._tcp IN SRV 20 0 5269 xmpp-server2.l.google.com.
_jabber._tcp IN SRV 20 0 5269 xmpp-server3.l.google.com.
_jabber._tcp IN SRV 20 0 5269 xmpp-server4.l.google.com.
http://www.google.com/support/a/bin/answer.py?hl=ru&answer=60227
http://code.google.com/p/jabber-net/wiki/FAQ_GoogleTalk