Hi Dave,
I'm trying to think how to do this, because usually, whenever I have reinstalled TB, I have just imported the mail from the previous version straight away, so the folders are overwritten, but nothing is lost, if you follow me. How did you come to have three separate profiles? Anyway, I don't think renaming the folders would work, as then it wouldn't associate your account with the mail folder. I can think of a number of ways to do this:
If you created a couple of new 'false' mail accounts, which don't actually do anything, then you could copy the new mail folders with the old ones, but that seems a bit messy.
You could open the old folders, and rename the files within them (i.e, Inbox2, Sent2, etc for one, and Inbox3, Sent3, etc for the other), then when you copied them to the TB mail folder, it should create separate Inboxes for the old mail. Again, a little untidy.
Alternatively, you could try this:
http://nic-nac-project.de/~kaosmos/mboximport-en.html. The write up seems complicated, but I have just tried it out, and it seems fairly straightforward. There is an option to overwrite existing mail, but this is unticked by default, so hopefully it won't, but I would strongly advise you to back up your current mail folders first, just in case, then at least, if this doesn't work, you won't have lost anything. I still think it will create an additional folder in your mail account, but I can't think of a way to 'merge' your mail folders in the way you would like.
Oh, one more thing you might want to look at is:
http://www.mailstore.com/en/mailstore-home.aspxHope that helps, Dave. There may, of course, be a much simpler way I haven't thought of.