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You really need to give more details then that in order for us to help. What OS are you using? What other hardware do you have (NICS,ROUTERS)? How many IP addresses do you have? (usually just 1)
How were you planning to set this up using the switch? Were you going to buy extra IP addresses and just plug the modem in your uplink port of the switch?
Are you going to put 2 NICs in one machine and connect the modem to one and use ICS or some other NAT/Proxy software?
Are you going to connect a one port router and have the modem connected to it then connect rhe 1 port to a regular port on your switch?
Are you planning to build a Freesco router and connect it to you modem and then to a regular port on a switch?
You see just buying a switch does not mean you are ready to share your cable modem. A switch does nothing other then connect your computers together.