Microblog-Purple (MBPurple) is a Pidgin plugin for Windows and Linux which integrates Twitter, Identi.ca and Status.net server through the conversation windows.
Microblog-Purple version 0.3 with OAuth support for Twitter has just been released. The package is not yet available in its official PPA, but you can install 0.3 in Ubuntu Karmic and Lucid via Frasten PPA:
sudo add-apt-repository ppa:frasten/ppa && sudo apt-get update
sudo apt-get install pidgin-microblog
To enable the plugin in Pidgin, go to Tools > Plugins and enable "Twidgin". Then simply add a new account and on the account type select Twitter, Identi.ca or Status.Net.
Using the plugin is very easy: you have a "rt" button, you can reply by clicking a username and so on.
You can also use the following commands in the conversation window:
/replies - to get all replies to you
/refresh - get new tweets instantly
/tag, /btag, /untag - automatically tag all your message, good for tagging messages with some hash tag (Example: #ubuntu)
For more commands, type "/help".
For other Linux distributions and Windows, download microblog-purple from HERE.