Make absolutely sure that you install the correct USB driver for the Empeg-Car.
I think that if you plug the car player into an XP box, by default, it gives you an option to use a built-in WindowsXP driver for "Rio". This is the wrong driver and it won't work with the car player.
In order to use the correct driver, you have to run the Emplode setup before plugging in the car player with USB.
I'm not certain about the above, and do not have XP handy to test it against. If you could check this and verify it, please give us any information you can, as I would like to add it to the FAQ.