I am the (un?)fortunate owner of a Compuke (sorry, but I really hate pee
seas) Presario 4814. Up at the top of the tower, it has an A/V line in, like
a stereo VCR or tv/monitor. What do I click on to display incoming video,
and if I don't have it, can I download it?

I can't see anything that says "display video" or anything equaly obvious.