http://www.icyphoenix.com/viewtopic.php?f=35&t=1592&p=11922#p11922
-----------------------------------
Mighty Gorgon
Wed 11 Apr, 2007 02:58

Re: Can I Copy Part Of Forum Structure ?
-----------------------------------
[quote user="ciufuliciboy" post="11820"]I need copy part of another forum phpbb to my forum icy last version.
Just I need copy one forum ( from 4 existent ) with all subforums but without message and permisions.
Just part of structure.
I have full admin acces to this forums.
Thanks![/quote]
If you are not so good with PHP I would suggest to import all the DB and then manually delete what you don't need.

It should be easiest.

Otherwise you may try playing with phpMyAdmin and export/import only the table for forums and categories.