There are rumors that Google will launch a Jabber-based IM service on Wednesday.
Neowin.net member Tom Servo confirmed that talk.google.com is an active Jabber server.
Last of all, you can login to the server using your Google account name and password with any Jabber client.
Several un-named Google Executives have confirmed that Google will be announcing "Google Talk" on Wednesday.
BTW, someone telnetted the server and sent an XML stream, and got an XML response, which confirms that talk.google.com is a Jabber Server.