The answer is simple:- even I was facing the same problem ... all u have to do is go to options on your webcam window, click on video capture filter, click on autoexposure type click on 50Hz, then click apply, then click on video proc amp, then click apply again, then click ok, and then rotate the black ring around your camera lens until you get a clear picture and there you go!
Abhinav
February 2007