Hi!
I have the same problem. All that Andre says is true. There is any
jabber client that works behind a firewall/proxy. The only client that
works it's the official GTalk that connects to talk.google.com:443. But
it doesn't use HTTPS protocol. Through Ethereal i've seen 2 mysterious
packets with encrypted data before the server start receive/send XMPP
(XML in plain text). The first mysterious packet is sent from client
which server responds with another mysterious packet. Anyone can tell
us what packets are those? Is Google allowing third parties use their
service on port 443??