user need to be reg. before it can open a thread

[thenight]

what I want is :

Guest MUST see the thread ( so he get hooked / intrested )
HOWEVER when he want to go into a thread he gets a no permisson you need to register to see the post.

With the option in CP now I can only turn of the Thread view, so the guest sees a empty forum so not much info that makes you feel like register or gives you any clue about the content.