Depends on the Modem. most Cable Modems connect to 1 computer and then can be connected to a Router which connects to multiple computers. I have a Modem, Then a Router, and also a wireless Router. I have a Vonage phone which requires a router. Then my wireless Router connects to all three and gives me wireless connection. So My Nintendo Wii, and all 4 laptops in my house connect. My suggestion would be to go purchase a simple Router. I would go to www.geeks.com they are priced great.
Check it out, & good luck