Setup ACL with two groups. The default group
users[/m] should have no (or only read) permissions, the second group [m]members has what you want to give your users. Eg. everybody can read, only approved users can write or upload:
* @ALL 1
* @users 1
* @members 8
Now put your email address into the register_notify option.
Whenever someone registers herself you'll get an email. Then go to the admin panel, choose user management, look for the user and change her group to
members.