To disable all your firewall settings build into windows2000/xp go trough these steps
first goto your network connections



Then select the network adapter what's connected to the same network as your xbox and get the properties



goto the advanced tabblad and make shure that the internet firewall is disabled
goto the general tab and select tcp/ip and select properties



then goto the advanced properties



goto the last options tab then and select the tcp/ip filter option and goto properties



then disable the tcp/ip filtering on all adapters...



if u don't want to disable then make sure that your configured port (1400) is listed in the tcp ports list