How to Connect an AirPort Extreme to a Cable Modemby Jason Taetsch
The AirPort Extreme router takes the signal from your cable modem and distributes it over a wireless area network so multiple devices can connect to the Internet. Use an Ethernet cable to make the connection between the modem and the AirPort router. Once the connection is made, the Airport Extreme will immediately begin sending out a signal to your Wi-Fi enabled devices.
Locate the "WAN" Ethernet port on the rear of AirPort Extreme.
Plug one side of the Ethernet cable into the port until it clicks in place.
Plug the other side of the cable into the "Internet" networking port on the rear of the cable modem.
Insert the Airport Extreme software CD into your computer's disc drive. Click "Next" and click "Install" to install the AirPort software to your computer. Open the "Airport Utility" and click the "AirPort Extreme" entry. Click "Next" to setup the wireless network for your home or office.