Hi help needed in new user registration

Hi
I am sorry if iam posting this in wrong section
i am having a strange requirement i have to develop in the following way
1. when the user clicks new user link it will redirect to another page where the users enters all the details (username, password, confirm password, department)
2.  when user clicks the submit button, it must insert in to database (or not) but must send new user request to administrator (in any way like using email or a displaying new user info in another page to accept or reject ) that a new user is registered and the main thing  user cannot login until the administrator approved his request
3. i dont know how to do this but i have to provide the above mechanism when the user wants to register
what would be the best way to so this 


thanks
...