Ubuntu Lucid currently comes with Thunderbird 3.0.x, but Michael found a nice way to install Thunderbird 3.1 on Ubuntu Lucid:
sudo add-apt-repository ppa:ricotz/ppa && sudo apt-get update sudo apt-get install thunderbird
That’s it.
You can find 64-bit versions of lightning (v 1.0b2) and the google calendar add-on at: http://releases.mozilla.org/pub/mozilla.org/calendar/lightning/releases/1.0b2/contrib/linux-x86_64/