I can attest to Duplicolor vinyl/fabric. It worked well for me. You will need multiple coats though. It is quite runny and the "paint" (more like a dye) absorbs into the vinyl the first coat or two. Krylon plastic paint has also worked well for me. Here's a few pics of my current interior project:
http://i843.photobucket.com/albums/z.../Photo0145.jpg
http://i843.photobucket.com/albums/z.../Photo0143.jpg
http://i843.photobucket.com/albums/z.../Photo0125.jpg