Sure, it's easy. You need a router, readily available from companies such as Cisco, Belkin, Netgear, etc. If you're on DSL or ADSL service, your service provider would have given you a DSL modem. If you're on cable service, your television/Internet service provider would have supplied a cable modem. Using an RJ-45 patch cable, connect the modem to the router's Wide Area Network (WAN) port, then with additional patch cables plug the PCs into the router's Local Area Network (LAN) ports. Start up the router first, then start up the individual PCs. Most Windows and Linux systems these days will automatically get a local IP address for your private network from the router, and the router will translate the local IP addresses into ones that the Internet sees. It's called "IP masquerading". Some DSL and cable modems feature a built-in router and multiple RJ-45 ports, so an external router typically isn't necessary for up to four PCs. If you get a wireless router, it will be able to handle four or so computers via RJ-45 patch cables and dozens of more devices via the wireless connection.