I downloaded Eudora:
http://www.eudora.com/download/
Using the Free version with ads, I was able to Import the mail files from Thunderbird into Eudora.
The twist was it would not see the actual mail files, so I used the
prefs.js file.
Using the Import function in Eudora, I specified the mail program as being Netscape Messenger and browsed to the prefs.js file in the Thunderbird Mail directory.
I was then able to Import the files from Eudora into Outlook Express.
Attempting to Import the files from Eudora into Outlook 2003 resulted in "The Mail folder could not be opened".
After Importing the files from Eudora into Outlook Express.
From Outlook Express, I Exported the files into Outlook 2003.
There were a few drawbacks.
Eudora created a folder for each file it Imported, I removed the folders to keep the clutter from being passed along.
I had several Profiles in Thunderbird, with each additional Import the previous Import was added to the next.
Import one Profile at a time, then remove the files from Eudora.
The Import appeared to Import the files that were in the Account directory in the Profiles directory rather than the Local Folders directory.
It was a bit complicated but *may* be faster than saving the messages as .eml files one at a time.