Installing Thunderbird 2 on Ubuntu was cake.

sudo apt-get build-dep mozilla-thunderbird
tar -vzxf thunderbird-2.0.0.0.tar.gz
sudo mv thunderbird /usr/lib
sudo ln -s /usr/lib/thunderbird/thunderbird /usr/bin/thunderbird

Then, just go to System > Preferences > Menu Layout, and add a new application launcher in Internet. The command is /usr/bin/thunderbird and the icon is in /usr/lib/thunderbird/icons/.

Enjoy.