I forgot to add that when I bought the router kit, the two USB sockets on the first PC were both in use.
As the Belkin router had to be set up using the ethernet cable first and I had no choice but to buy the card, I kept this connection method.
Once it was working, I could have replaced the ethernet cable with a dongle connected to a USB hub, but obviously this second dongle and hub would have been a needless additional expenditure. Besides, the ethernet cable is hidden from sight.