Another way to do it would be...
Put a second network card in one PC. Connect that PC to your Internet connection with one of the cards. Plug the other card into a hub. Plug the rest of your PC's into the hub. Then one PC works as a server and you will have more security than you would with a router. If you disable file and print sharing on the internet network card and enable sharing on the card going to the hub, then you will have a private network between your PC's that is not easily accessible to the outside internet.
