You can restrict users now within a group for the forums that they can post in, although in 7.3 you will be able to restrict a group to much tighter controls.
At the moment you are restricted pretty much to limiting which forums the group can & can't see & which they can post in.
7.3 will expand group permissions a great deal.
It is also worth mentioning that you will benefit from upgrading to 7.2.2 as several bugs have been fixed since 7.0 and several new features introduced.
