Hi Liz,
I just had a look at the link... I have to say, there's not really much there that entices me to sign up.
Because I have been around the Forum Software block a few times, I can assume that several forums would appear to me if I did, but your average punter is probably going to be unaware of the benefits of registration.
Hiding your content from guests can be a very bad idea. If they can't read the discussions, they won't know whether or not they are within their own genre. Would you have signed up to
NZB if it had just been a logo and the 'Whats Going On?' box?
If you really want to keep them hidden, some suggestions are: a) Have a 'Guests Forum' where people can get a feel for the site, or b) (and this is essential, IMO, even if you do allow guests to see the discussions) have a banner/box/something that describes the site and what it does and why the guest should register.
Head over to
www.theadminzone.com if you haven't already. It is by far the most helpful site that I know of when it comes to providing newcomers with hints and tips on community administration.