ok, now i understand *g*
so:
if you go in your admin cp to "Add new Forum", then there are some things to fill in, for example:
Title
&
Description
AND
"Forum Parent"
The You can said, that it is an category if you
DON'T SCROLL DOWN on this feature.
If there is "No One" in your scrolldown, right of "Forum Parent", then it's set as an category!
hope i could help you with my bad bad english
cYa!