Keep the current version of FW thats loaded.
Need to review the Gaming, QoS and Gamefuel sticky for XBL to configure Gamefuel for use with XBL. This will help you get connected, host, chat and game.
How fast is the wireless ISP service you have UP and DOWN? Some wireless ISP are not good for gaming just FYI.
To tell if the modem is bridged or not, look at the 4500's web page, Status/Device Info/Wan Section, if there is a 192.168.0.# address in the WAN IP address field, then the modem is not bridged.