Thank you for your replies. After further investigation, I have found
out that it is indeed a problem with the firmware version on the Netgear
DG834 router that I have.
Apparently, multicast is enabled only for wireless to wireless or
wired to wired connection on this router. It is NOT enabled for wireless to
wired or wired to wireless connection. So in my setup, the Soundbriges
which are connected wirelessly to the router, can see the server on the PC
which is also wirelessly connected to the router but cannot see the server
on the NSLU2 which is wired directly to the router. This issue has been
raised on the Netgear forums so hopefully it will be fixed by them.
(see http://forum1.netgear.com/showthread.php?t=1212 )
Also, I would like to thank you for the what I have found to be
the best media server for the Roku Soundbridges. I am particularly
impressed with the speed, reliability and the ease of use of the server.
Keep up the good work !!