Sure, Thunderbird stores the e-mail in the mbox format. I believe that
all you have to do is to add the .mbox extension to the corresponding
files and you can import them by drag and drop in Entourage
Now I feel kinda dumb. I should have searched the Web before posting
here. Found a good set of instructions at http://www.riches.com.au/articles/export-outlook-entourage.htm which
actually described moving Outlook to Entourage with Thunderbird as an
intermediary. It worked flawlessly.