If Gmail, iGoogle, Google+ or orkut do not seem to be capturing your webcam, please check that it is properly plugged into your computer and that no other open programs are using the camera. If this is not the case, there may be a driver issue. If your camera name in voice and video chat settings comes up as USB Video Device, this means that you are using the generic Windows camera drivers. Installing the correct drivers for your model of camera will likely fix the problem. Also, most camcorders are currently not supported.
Please also check that the voice and video chat plug-in is using the correct webcam. Learn how to verify your settings.