Memberarea with private!

Hey folks,
I want to install a memberarea on my site. I thaught about using private!. I want to have the most pages availeble to all users. There should be some pages that are only availeble to certain users.

E.g. I have group a, group and group c and the following pages page 1, page 2 and page 3. Now, i want group a to have access to page a. Group b to have access to page 2 and 3 and group c to have access to page 3. These groups should be easy to change, to give more rights e.g.. If i take some pictures on a company celebration i want to enter all coleeges to group a and give them permission to page a. Other groups should have access to more site.

How can i do that, i got no clue. I activated private! But there is no such options. There is only open site with paid memebership. Do i have to take this?

Winam