Could it be possible that the full set of phpBB2 files aren't necessary and that the database and the phpBB2 config.php could be sufficient. I'm thinking along this way because both 3.3 and 2.0 need to be "installed on the same server but there is no php version on which 3.3 can run,together with 2.0
If not, completely reinstalling the phpBB2 board would be necessary (using an old Easyphp or Xamp version with which 2.0 and 3.0 can run).
Hmm?, can't find it but not all that long ago there was a topic with links to very old versions of phpBB (down to 1.4.4 even, or earlier).
Found a 2.0.4 http://www.oldversion.com/windows/phpbb-2-0-4