Requirements for an Access Software

Hi everybody!

I would like to find out about the requirements for a youth hostel internet access system. I have written a program for the youth hostel in Plakias, Crete, which I would like to make available more widely to youth hostels elsewhere and would like to know whether the system as it stands fulfills more general requirements or what I would need to change.

The system I wrote for Plakias is a little program (for windows 98 or XP) running in the background which communicates with a webserver. As long as the computer is "locked" - the program will keep a browser-window (IE or Firefox) open which displays a login-website on the webserver. It will also not allow to start any other (restricted) software on the computer.
The browser will also not allow to open a different website.
After the computer is "unlocked" the access for other websites and programs (e.g. Skype, a messenger program, a webcamera...).

The administration for the hostel manager is password-protected on the webserver. Several computers can be controlled by the same webserver.

The question for me is now about the way how people are charged:

There would be three possibilities:

1.) Every guest can create their own user-account on the webserver which allows them to log in on any hostel-computer to access the web. They will just need a PIN from the manager once to create the account (with a username and password of their choice). They will be charged later when they leave the hostel. The manager will get the access information from the webserver.

2) The public computer will be unlocked by the manager from his desk (central computer) and the manager will charge the guests when they leave the computer.

3) The guests buy PINs with a certain value in advance. On the login-screen they will enter a PIN and then they can use the computer until the value is used up.

Of course it's possible to combine 1+3: Creating user accounts and adding value to the account with PINs.

What would suit people best?