Is your webcam not showing up entirely, or just not taking pictures?
Open QuickPlay, then click the icon that has pictures, headphones, and a movie reel. When the new window opens, click on webcam under the sources list.
I have also seen other users have problems with the QuickPlay 3.2 not listing webcam as an option. Try going to the QuickPlay update screen and download the 3.7 version, now everything should work. So if the above directions don't work, try the update.