This hack will allow you to set a post count on a forum per forum basis for your members to order them. This can be also done with group promotion but like this it is way much easier and handier in my opinion.
Anyway, after you install the mod, go to your Acp->Forums & Moderators->Forum Manager. Chose the forum where you want to allow entrance based on post counts, click at Edit Forum and all the way to the bottom, you will see a new setting that says: Miscellaneous Options. Enter there the number of posts that you want your users to have for entering that particular forum. Administrators, Super Moderators and Forum Moderators are automatically exluded from the number of posts limit.
The Spiders are not affected by this as well btw.
For more information, please have a look at the attached screenshot below.
Screenshots:
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