You should have sorted this out a long time ago!
It's really unclear from your garbled description what you're looking for.
I *think* what you're looking for is a 15 meter VGA cable - you can get them from computer shops (PC world etc). It's slightly specialist, and usually I'd order them from Amazon etc.
I don't know what this 'yellow' cable is - do you mean a composite cable, ie. the connector has only one pin in the middle, or a S-Video cable (connector has about 8 pins in it, and a plastic bar so you can't plug it in wrong way around)
Your powerbook probably already has a S-video output on it, and it should have come with a s-video / composite converter (5 inch cable with 2 small connectors on either side). If you've lost the convertor, you can get it from an apple shop, or maybe your local hifi / home electronics shop will stock some for a couple of quid.