Google has connected the Google Talk network to the public XMPP network.  What this means is that Google Talk users can now communicate with users of any public Jabber network.  To make it work you just need add the address (ie user@jabber.org.au) of the jabber user into the ‘add friend’ link (it used to be the ‘invite’ link).

I just added myself to my Gtalk list and it worked fine (messaging yourself is kinda lame though).  The only restriction is that the Jabber server that you’re connecting to must use the dialback protocol.  Aparantly all the servers listed on the Jabber site work, so that’s a good start.