Elgin,
since Thunderbird is a Mozilla-based client, you would select "Mozilla" in Mail's import dialog. However, since Mail's import function from TB has some shortcomings (it doesn't deal with Windows and older Mac files, you will lose all your message status flags, ...) you might want to take a look at Eudora Mailbox Cleaner as an alternative (and imports messages from TB to Mail as well):
http://homepage.mac.com/aamann/
i Andreas
since Thunderbird is a Mozilla-based client, you would select "Mozilla" in Mail's import dialog. However, since Mail's import function from TB has some shortcomings (it doesn't deal with Windows and older Mac files, you will lose all your message status flags, ...) you might want to take a look at Eudora Mailbox Cleaner as an alternative (and imports messages from TB to Mail as well):
http://homepage.mac.com/aamann/
i Andreas