Does the camera turn on when you start Photo Booth? The green light next to the camera lens indicates that the camera has power. The light will go off when you Quit Photo Booth.
Have you tried downloading and installing the combined 10.4.8 updater?
http://www.apple.com/support/downloa...dateintel.html
this is a valuable trick to try after doing the software update to a newer version, and some part of the system gets a little wacked out.