Well, yous hould do your database design first, then do the code, it is alot easier that way.
For example, you put fields such as "activated"(1 or 0) and "level"(level of access, admin or whatever) in the users table and then in the one where you pull out the info. you just pull out all the info WHERE activated = 1 meaning it will onyl pull out the users that HASNT been actviated and when you do click activate, it will set it to 1 or if you want to deny, you can delete it. But whenever a user registers, the admin should get an email containing a link to a page such as "http://www.mydomain.com/members.php?action=activate&uid=6 " so it will pull up that persons info and give you the options, but you should secure all the pages.
Hope this helps