As I posted earlier today, Google is exptected to release a chat client within the next few says (although most sources point to Wednesday). However, there are already scores of people making use of the Google Jabber server at talk.google.com in their chat clients (GAIM, Trillian, Adium and iChat).
Here is how to do it.
Username: [email protected]
The server seems to be going up and down randomly.