Is there a mod that will alter permissions based on rank?

What I would like to do is have a special forum on my bulletin board that is unique from the others whereby it is only accessible to members who have posted a certain number of times.

One solution I thought would be to make users who have posted a certain number of times automatically added to a group that has permissions to access the special forum...but I don't think that's possible.

Is there a Hack that does this or somehow otherwise accomplished the same objective?

This is for the latest PHPBB2 not 3.

Any advice would be appreciated.