Thanks for those comments, aay. Indeed, I had a look around and discovered that there are a lot of early, cheap webcams about that contain either the CPiA or OV511 sensor. These, apparently, can be a whole pile of trouble! There are other Linux apps to try: pwcx, xcam and Gnomemeeting, but if the others don't work and the cam doesn't appear in the lists, not a lot of hope. [I have since discovered that 'doze users also have their own webcam problems - there's a good chance that an error message relating to MMSYSTEM006 will show up. None of the third-party suggestions given on the web or the 'official' fix are guaranteed to work. This is a SW issue (of course!)].
Any and all additional suggestions very welcome. Thanks.