Webcam testing application?

"you can take a still image with MS Paint (File > From Scanner or Camera... - this will get you a live camera preview, without sound).

if you want to do a quick recording to check the volume level of the microphone, you can use Windows Movie Maker (not all versions of Movie Maker support capture from camera, this portable version does).

if you're looking for something more specific:

WebCam Monitor provides an intuitive user interface to preview the video from your camera. The Preview screen can be used effectively to position your webcam to get the best results while monitoring.

WebCam Monitor is shareware ($69.95), try before you buy."