If you are interested in the iTrip - depending on where you live, I wouldn't bother. The iTrip works by "hijacking" an unused radio frequency and transmitting your iPod playlists over that frequency. They were only recently introduced in the UK, as they were seen as Pirate Radio. I think you can get them now, but if you live in London, for example, finding an empty radio frequency is near impossible.
Good luck.