Now, No need to download and install Gtalk.
Gtalk is now available online without downloading and installing its client software, just go to http://www.google.com/talk/ click on “Launch Google Talk Gadget” and start Chatting with your GMAIL friends.
Clicking on that link will popuo a new small window with ready to use gtalk, if you are not logged in to your GMAIL account it will ask you to Logged in first and then just start chatting.