I have done this on my Ubuntu 10.04 and it works, Just follow the simple steps:
- Install the extended preference plugin
sudo aptitude install pidgin-extprefs
- In your Pidgin click on Tools > Plugins check the “Extended Preferences 0.7″ > Configure Plugin > check “Hide buddy list at startup” and close.
- In Plugins check the “Buddy List Options” > Configure Plugin > check “Hide the buddy list when it is created” then close.
- System > Preferences > Startup Applications > Add.
then you save and close.
Name: Pidgin Internet Messenger or "any thing you want to type".
Comment: "anything you like to type again."
Enjoy and have fun with your Ubuntu.