Thanks, Agent86, but I am still puzzled;
If I share a directory on my PC, it will be visible to any other PC on the internal network regardless of whether my PC, or any other, is connected to the DG834G via wireless or ethernet.
Given that the ADSL line is connected to a third party modem and is then being transmitted via ethernet to the DG834G, I would expect it, too, to be visible regardless of whether I am connected wired or wireless.
A couple of years ago I did exactly this with the DG834G and my BT Home Hub. For reasons irrelevant to this thread I used the Home Hub for internet acces but (via ethernet between the two) the DG834G for wireless connectivity. The only difference I can see compared to the situation I have today was that I used the Home Hub for DHCP allocation of IP address so switched this service off on the DG834G.
BTW - Thanks for the utility link. It doesn't help me today but I have bookmarked it for future use.