My router 'default' is to block inbound and outbound. In my setup I've set up xbox as a service on TCP/UDP:8088 (8088 being the port). Then added it as allow always for both inbound and outbound.
In WAN setup what's your MTU setting, make a note of it and try 1492, if that's not the current setting, you can change it back.
In basic settings, is your NAT enabled?
In case you haven't tried the MS pages:
http://www.microsoft.com/windows/products/winfamily/mediacenter/extenderfaq.mspx
http://www.microsoft.com/windowsxp/mediacenter/extender/setup/ssviewer.mspx
In WAN setup what's your MTU setting, make a note of it and try 1492, if that's not the current setting, you can change it back.
In basic settings, is your NAT enabled?
In case you haven't tried the MS pages:
http://www.microsoft.com/windows/products/winfamily/mediacenter/extenderfaq.mspx
http://www.microsoft.com/windowsxp/mediacenter/extender/setup/ssviewer.mspx
