I see. Thats done the trick. Many thanks!
I am writing this in our observatory while my better half tries to fix a dodgy connection at the back of the camera. It appears at the moment that this may be the reason why we are getting intermittent colour. We have had both colour and B/W tonight depending on tiny movements of the S-VIDEO connection (with WinTVUSB/2K). So it appears that this may be the problem not WinTV!!