I am switching computers and needed to migrate my Thunderbird email client data to another machine. I did a little googling and did not find too much until I found Thunderstor It allows you to take your thunderbird account and exprt to eml files. Then import into system of your choice.
If you are moving from one thunderbird account to another you can also just move your profile. It is located at c:\documents and settings\yourusername\application data\thunderbird\profiles\****.default
I migrated those files and then pointed the profile.ini file to my old profile. All is well