Using a database is by far the most efficient way to do this. Here's what I recommend doing:
Database:
1) Create a database
2) Assign a user to it
3) Create a table that will store all users, indicating somewhere whether or not they are an administrator
Web-end:
1) Create a form and a way for them to register/login
2) Have them insert whatever data it is you need when they register
3) Create a form processing page that will insert their information into your SQL table
4) Create a page for administrators to add new administrators
5) Create a page for administrators to view user info, using a get variable and a url to associate a user with the page
6) Make sure that when the variable doesn't exist, a user list pops up
7) Use the get variable and retrieve data from the database
8) Display the data
Using PHP and MySQL this is quite possible. If you need more help, just say so.