Anyone having issues with old PMs not in your inbox, create a folder, and they should appear in that folder, this was just a bug on the import.

Go here:
http://www.dual-boxing.com/private.php?do=editfolders

Under Add New Folders, add 1 folder, name it anything other than "inbox". Hit Save Folders, and go here: http://www.dual-boxing.com/private.php

And see if the folder you created is in the drop down, it should be, and it should have your missing PMs.