I have it set so that people under x amount of posts can't post or view in certain forums using the forum hack.

I also have the Last Post thread hack.

Users can totally bypass the "can't post if you don't have x amount of posts" by clicking on the Last Post thread link.

Kind of defeats the purpose

look: http://php.stileproject.com/spf

try posting from the forum link then last post to thread link.