Well most TVs nowadays have DVI and VGA ports, which work with whatever Powerbook G4 you're talking about (be specific!). Just make sure the TV you're getting has support for whatever video-out your G4 has.
Not to be nudge or anything, but you do know that plasma's suffer heavily from still image burn-in and whereout? If you keep a computer on it, its going to show a still image (one thats not moving, in a movie, al the pixels constantly move/change color...etc), very very soon, especially plasma will where out from it and you will eventaully your image will fade away, since all the gas bubbles are fried and worn out. I would recommend a LCD or a DLP, they are the only two TV's on the market that are not afraid of still image burn-ins.