The best way would be to purchase a device called "residential gateway" or "router". Most of them come with 4-port Ethernet switches on board, so, provided by your PCs have Ethernet network card, you will be able to connect them to the router. The cable modem gets connected to the router's "WAN" interface. For a better coverage of what's beyond just physical connections you have to make, visit http://www.homenethelp.com . This guys have a great deal of detail of the subject.
Dmitri Abaimov, RCDD