All ran as configured. There's a switch 'SUBFORUMS_TO_FORUMS' in the script which is set to 1 by default. Value 1 makes all discus-subforums mainforums in phpBB. This is because phpBB2 doesn't support subforums. After converting phpBB2 to phpBB3 you can then manually convert this main-forums to sub-forums (their hierarchy can be told from their name, like 'forum a :: forum b :: forum c' means forum c is a sub-forum to b which again is a a sub-forum to a).
This switch was introduced keeping the new possibilities of version 3 in mind.
If you prefer removing your sub-forums and consolidating everything under the main-forum, you have to alter the switch SUBFORUMS_TO_FORUMS to value 0 and re-run the whole script (takes a couple of hours).
The redirector script can be found under http://www.discusscripts.com/downloads/redir_discus.zip
Unzip it and upload it to an arbitrary directory (such as the "discus_conv" directory I created for you), configure 'redir_discus.php' and run it. Keep in mind you have to run the redirector after a new run of the discus importer script. Also, the discus passwords won't work in phpbb, your users will have to get a new one. As a convenience, you may overwrite the original login.php script with the one in my .zip file; this will allow the reuse of discus passwords, but only in version 2. If you migrate version 2 to 3, users will have to get a new password anyway.