Locking forums for guests?

[Chruser]

I know there's a possibility to lock up the mainpage of the forums, so the guests HAVE to register before being able to view the forums at all. Also, you can "hide" all the forums for guests, which will make the forums look empty.

My question is, how do you let users access the "mainpage" of the forums, so they can see the cathegories, while they would have to sign up to actually see what's in a cathegory?
I think this could be done with some very simple coding, maybe even some option that I missed, but it would be great if you could help me (I know more people looking for a feature like this).

[Admin]

Chruser, please go to this (http://www.vbulletin.com/members/vbulletin.org.php) page and enter your username, to show you are licensed. (you will need to use your customer number and password to access that page)
Thank you.

[Chruser]

What? You need a licence for the forums now?
Haha, j/k, I'll ask the owner as soon as he wakes up. He's probably going to be mad at me if I wake him up at 3 am though. :D

[tmod]

So how do I lock the forums for guests and still have them able to view it?