PC-to-Television doesn't fill screen

Greetings. I am playing an .avi file using Nero Showtime to my TV set (S-video, sometimes RCA jacks) from my PC. The picture doesn’t “fill” the TV screen with black space on either side of the movie. Is there a resolution or output device setting to correct this? TIA. Regards.

How big is the black space? is your TV out card nvidia?