When running "xawtv -c /dev/video0" returns errors about the device not
supporting overlay mode, and the xawtv window stays black, you can try the
following command line:

xawtv -noxv -remote -c /dev/video0

This will give you a picture, because it disables XV and the overlay.
The reason for not working with XV extension and overlay may have to do with
a bug in the Nvidia proprietary driver.