Use Twitter in Pidgin (download for Windows, Linux and of course a Ubuntu package)
Previously, the way to connect to Twitter using Pidgin (IM client for yahoo, google talk, msn, etc), was to use a jabber account like google chat, then add Twitter. But Twitter shut down the Jabber service. So it doesn’t work anymore. But now, Pidgin-microblog can do the trick.
You can download it from here (.exe, .tar.gz and .deb for unbuntu).