Fear not. Not evrything is lost, though you've managed to get a whole lot of work for yourself. Even that depends on the amount of accounts and folders you had.

You keep mentioning the directory MailPwd, I suppose that's your old mail directory as TB calls it?

In your mail directory you'll find a directory for each of your accounts, those directories each have the same name as the matching account.  Are those directories still intact? That would lighten your workload a lot. I'll presume they're still okay and tell you what to do from that point.

Install TB
Run TB
Enable OTFE (On The Fly Encryption) and use the same password as before (that's important)
Create your accounts, to prevent any problems give them the same names as they had before in your old setup.
Don't download any messages yet.
Close TB.
Copy the contents of your old mail directory in your new mail directory.
Keep your fingers crossed and start TB. (You should be able to double click the left mouse button with crossed fingers )

Install TB and don't download any mesages? Yes, because his trick will overwrite any existing new messages. I case you already downloaded somenew messages, select them and export them to a safe location in the unix mailbox format.

You've already installed TB wit a new password or with no password at all? Too bad. Export your new messages and uninstall TB, you can only change the password by installing and uninstalling TB. And you need the original password as that's the key to decrypting your old data.