Restritct Internet access

The easiest way to do this is simply to go to internet properties and change the proxy to something non-existent .
Tools > Internet Options > Connections > LAN Settings > Use automatic configuration script
ANd then type anything there ( http://internetblock.xxxxxx)
only a knowledegable person can change these settings .
for additional security you can password protect internet properties so even if someone knows how to change proxy settings then they need a password to change above settings.

hope i answered you question !

Most routers, even cheap ones, have a MAC filtering mechanism to allow [or] restrict internet access. Check if your router has it, and how it filters ie: is it Positive (set to allow MAC addresses you enter and disallow all others) or is it Negative (restrict addresses you enter and allow all others). Most routers are negative filters - they restrict the computers MAC address that you enter.

Next you find the MAC address of each adapter on the computers you want to allow [or] restrict, then enter it into the router's corresponding MAC filter.