I wouldn't completely rule out a connectivity issue just yet. More diagnostics to do first.

Lug the receiver into the same room with the Windows XP box and plug it into one of the ethernet ports on the Belkin F5D7234-4.

Does it work then? You've got a connectivity issue with that linksys bridge, despite the fact that you can ping the receiver when it's connected.

Plug a laptop into the linksys bridge and turn off the laptop's wireless networking features. Can you surf from there? Try streaming some audio.

If that all works, try, with the laptop plugged into the linksys bridge, to query the Receiver Server from the web browser. The specifications on how to do that were here, but unfortunately Roger's web server appears to be down so I can't give you the instructions on how to do that. Perhaps someone can chime in here with those instructions.