I have installed a Belkin G Wireless Modem

You have to configure your router's wireless setup. To do that, you need to connect you computer/laptop to your router using ehernet cable (cat5). Once you're done, open internet explorer/firefox and enter your router's ip address (can be found in your manual or at the back of your router), you will be ask for username and password (just enter the default if you dont change it before, username: admin , password: none/blank. depends on manufacturer). After you provide and entered those information, you're now on the setup proccess. Just go to wireless setup menu and select your options there. Remember, enable DHCP for the router to automatically assign an ip for your computers. Goodluck!