After installing Ubuntu, I immediately see the chat balloon (Indicator Applet) next to the clock. I entered my Google Talk user name and password there (left click > Chat Accounts), but the status is always smth. like ‘disconnected, no reason specified’.
This is solved by installing Pidgin:
sudo apt-get install pidgin
and configuring it for Google Talk account. After that the same chat balloon controls the status of the Pidgin’s Google Talk. To see the contacts list, I have to run Pidgin with Applications > Internet > Pidgin Internet Messenger.