Hi,
As far as i can understand you would want to disable internet access to some systems who just use LAN for multiplayer games, this could be done in two ways
First you can setup a access control on the router from which you can enable or disable internet on the systems based on IP from time to time.
Secondly in case your router does not support access control then set up a proxy server and this in turn can be used to enable or disable internet access to systems based on IP.
Hope the above solutions should be of use, Else we can offer you an appliance which will be a total solution for your internet cafe please call me to know the pricing.
Thanks and Regards,
Saraswathi Infotech
+91 9900631718
www.saraswathiinfotech.in