The 15" powerbook should have both a full size DVI port and an s-video port onboard next to it. If your tv has s-video inputs, that's the way to go. You will need the s-video cable and a cable for audio. See if you have an old minijack to rca/component (red and white) cable.
If the tv does not have s-video inputs but has composite (red/white/yellow) then you need the same audio cable but you need another adapter which the powerbook may or may not have come with. I'm not sure exactly which cable it is but it should convert either the DVI port or the s-video port to the yellow rca style cable. On my ibook I needed to buy a mini-vga to composite and s-video adapter, but since you already have s-video I'm not so sure what yours would look like.
If you need the adapter, and its not included in the box, go to an apple store at the end of the month and see if you can get one on the refurbished/returned table. Most of the cables that end up there are from people buying the wrong one and it gets you a nice 50% off. I got my cable for $10 instead of $20 and it works perfectly.