Or consider
Portable Thunderbird 1.0.5 (USB Drive-Friendly)
http://johnhaller.com/jh/mozilla/portable_thunderbird/
"Portable Thunderbird is a fully functional package of Thunderbird optimized for use on a USB key drive. It has some specially-selected optimizations to make it perform faster and extend the life of your USB key as well as a specialized launcher that will allow most of your favorite extensions to work as you switch computers. It will also work from a CDRW drive (in packet mode), ZIP drives, external hard drives, some MP3 players, flash RAM cards and more."