• Set up one computer to act as a gateway to the net.
• When a customer buys time on a PC, add that PC's IP to the firewall's "allowed" list.
• When customer's time is about to end, send a windows message to that machine so that they can either save their work or buy more time
• When time's up. Remove/disable that PC's IP in the firewall.

• Find firewall/proxy software that would allow you to update its configuration programmatically and/or via a command line utility
• Setup the firewall/proxy
• Write a small Perl daemon for keeping track of usage times (this is probably the easiest part)

Er yes. It incorporates both your internet cafe request and the thing on controlling other computers.

#!perl -T
use CGI;
print
    start_html,
    p( "Another coffee please! Oh and go tell someone to turn this com
+puter on" ),
    end_html;
[download]

Now maybe you'd like to be clearer about what you mean. I thought you were entirely opaque.

I did a search on google.com trying to look for a "Internet Cafe" Program, there are numbers of commercial products out there, but sincerely costly, because once you purchase one kind of program (software, and they are not cheap, you are attached to it forever because of the clients that you have to buy every time you add one extra computer to the network. My alternative is to look for a perl program that I could implement my own way. Thank you!!!!

Isn't lock-in a wonderful thing?

I don't know of any existing Internet Cafe programs for Windows written in Perl, and if any exist I think they would be expensive. Odds are that you won't succeed in writing one easily either because writing a good one requires hooks into Windows that you are unlikely to find freely available. But if you have to charge anyways, vendors won't find it easy to ignore the potential cash cow from lock-in, resulting in what you have above.

Standard advice for customers who can't avoid lock-in is to use the fact that both you and the vendor know that you will suffer in the future to get a sweet bribe up front. (For more details, read Information Rules.) Otherwise assess your pain, and think about whether or not you are willing to go with an alternate solution. For instance the Linux Terminal Server approach can be used to create an internet cafe - but some customers will be turned off because it won't be Windows. You might be able to make it Windows using VMWare on top.

There are more options, I know. I don't know what they are, but I do know someone with the necessary skills who did some research into starting a business like this but then decided not to. I don't know what he found, or what his reasoning was though, but create an account and ask me privately and I will pass you his email address. (I don't want to post it publically for obvious reasons.)