These links help quite a bit in getting google talk working with xmpp. Using a gmail.com domain for a jid is very different from using a gmail address with your companies' domain.
You need to setup SRV records on your DNS server.
http://victortrac.com/taxonomy/term/112
http://kingant.net/check_xmpp_dns
http://www.olark.com/gtalk/check_srv
There will be a Drupal module called jabber published shortly with the work I'm doing here at Babson College connecting Drupal to google talk, well any XMPP server really.