That is the cheaper way to do it. However, the best way is to buy a router with more than one built-in ethernet port. This router will add a "hardware" firewall to your home LAN. In this configuration, you'll end up buying a $100 router (I recommend Linksys or D-Link) and you'll only need a total of 2 NIC cards. The router acts as the interface between the PC's that are connected through it. If you follow Cirrus9's suggestion, it will work just fine too with the lack of security. Software firewalls are great, just not as secure...