Let me add to this a little bit:
1) Power down (unplug) the modem, the dir-655, and your computer equiment
2) From the back of the cable modem, locate the ethernet port and plug in a ethernet cable
3) Take that cable and connect it to the grey internet port on the dir-655
4) Plug in the cable modem's power cord; count 30 seconds then
5) Plug in the dir-655's power cord
6) While the dir-655 is booting, plug in another ethernet cable to port 1
7) Plug in the other end of that cable into an ethernet port on one of your computers
Power that computer on
9) Launch a web browser. You should be on the internet now.
10) If so, visit http://192.168.0.1 and login as either admin/admin or admin without a password
11) Go thorough the Setup -> Wireless Settings -> Wireless Network Setup Wizard
12) Set the options you feel necessary
13) Save those settings, reboot the dir-655
14) Connect Wirelessly with your other computer with its USB 2.0 wireless device
If something doesn't work at a certain step, backtrack and try again.