I have a local area network with some computers and different OS (Win98, WinXP, Win2000, WinMe) using the Microsoft Net client and TCP/IP protocol.

The conexion with internet is made with a DSL Router.

Every computer has connection to Internet, however, How can I make certain computers to have access to the LAN only but not to have access to Interntet?

In other words I have A,B,C,D,E computers in the LAN. I want everyone to have access to the shared files of the others but only A and B to have access to Internet.