Sounds like a bad driver. Have you tried "rolling around a driver", (RAAD)?
For example if your webcam is a: 1100a, then try: 1100b or 1000c.
Also try NOT using the driver that came on the CD with the webcam, often these drivers are very old by the time the customer actually purchases the product and an update/revision has been made months before.
Check at the manufacture's website for updates to the driver and firmware.
general thoughts.
