set up private forum

What is the best way to set up a private forum?

I am designing a message board that Guests can read the rules and that the Forums exists as a benefit to members of our organization, inviting them to become a member. Then I have password protection on the individual forum topics.

But what if the quick-to-click viewer registers and THEN finds out that they can't access any forum topic without a password? And what if there are lots of these? How can I keep my database maintenance from becoming a nightmare?

I understand what you're saying, but ....

I was thinking that I could offer the password to all paid members upon registration, change the password once a year to make them keep their dues up. (This forum would be just one of their benefits.)

Anyway, another surfer would stumble upon the forum, register without reading the rules, curse because they don't have a password, read the rules, not want to become a member, never come back, and their info would be taking up space in my database.

That's what I'm saying.