Limited guest posting

On one of my sites we ahve certain topics that we would like the guests to be able to reply to. These are topics concerning are reviews, news, etc. I however would now like guests to post everywhere. Only the threads I say they can. Is there any hack like this? If not anyone willing to make one? Thanks or anyhelp

maybe try making a reviews forum, and allowing them to only post in that forum, leaving the rest not allowing unregistered users.