I have found that the Belkin Wireless G router, and perhaps other similar Belkin routers, does not reset the "WAN MAC Address" when it performs the Restore Factory Default function. I had a problem where a cable modem would provide internet into a computer, but the wireless router refused to pass any packets. It turned out that the WAN MAC Address needed to be set to the MAC address printed on the sticker on the bottom of the device. So if you have a Belkin Wireless G router, and even after doing a Restore Factory Default, you still have trouble connecting to the internet, look for the MAC address on the sticker on the bottom of the router and put it into the WAN MAC Address setting.
So I just want to make this point because it was frustrating: Belkin sold a device with a feature with an explicit promise, and the device fails to hold up that promise. When resetting the device to factory defaults, it does not reset all the settings to factory defaults, as it should, since that's what it promises.