Some video cards will modulate to an unused NTSC channel or output composite or S-video. FOr most PIP TV sets, a composite video feed is be used as one of the PIP inputs and is also better than an RF feed.
By the way, internet into a PIP window is extremely poor picture quality. It is still the 640 x 480 or whatever the computer is putting out except scaled to perhaps 160 x 120 with the obvious reduction in sharpness.
Better to do POP, put a computer monitor next to the TV if you can find a space not too close to speakers and their magnets. If you have "Sound of Music, view the scene with the home theater, with the soundtrack playing the number "Lonely Goatherd".
Video hints:
http://members.aol.com/ajaynejr/video.htm
