I'm not explicitly familiar with your situation, but are you saying that the source of your broadband is a USB device? If so, you need an always-on computer effectively to be your router. Assuming this device shows up in your network settings, you can turn on internet sharing and tell your computer to share this connection over ethernet. Connect this to one of the LAN ports on your linksys, and turn OFF the DHCP server on the linksys, as your host computer will become your DHCP server and router. The linksys will only be a switch/bridge.