You can trouble shoot this the other way around as well. Do you have a video camera, game console, or something else that will provide s-Video input? That way you have a device you know works, and that the TV/VCR system is set up correctly.
I know that in my own home, the number of inputs, boxes, and outputs things have to get to to get to the TV, or the Stereo, is quite complicated, and borders on rocket science 😉
Alternatively (though this may be what you're doing) try and plug you Powerbook directly into a TV, and simplify the equation that way.
~Earnedil