If your admin in the forum, then you can make change to it.
I think what your trying to do is get people to post in the sub forums and not make a new topic in the category it self, If thats the case you just got to change the Main part of the forum to board
and then the 2nd level to category, and then third level to forum.
Then it will look like PHPBB And Vbulletin style Forum.