Thanks for the replies chaps!
I think that the problem referred to by the original poster is that if the USB interface is provided by an add-on card then any power supplied to the webcam will ultimately have to come via the PCMCIA interface. That could result in the available current being less than you would expect to be available from a motherboard USB port.
That sums it up better than i could have! The laptop is great, but old and Mrs SHJ doesn't want to spend loads, as after a certain point it's easier to bite the bullet and go for a new steed. I wouldn't have thought that a webcam would draw too much current, but it seems as if this might be the case.
SHJ