memory stick mp3 player

I wondered if anybody had tried these mp3 memory stick players available, they basically plug into your cigarette lighter and you then stick a mem stick into it and tune into a frequency on your radio and hey presto it plays all your mp3s on your radio, well it would if it worked! My car wont pick up the signal, I wondered if it is because ithe radio is on the computer and not a conventional receiver. Anybody else tried it?
WillM5AD