There are a couple of ways you can do this. Using an FM transmitter such as the iTrip will work fine, if the iPod is close enough to the radio. Unfortunately, fifty feet is too far – no FM transmitter is going to provide a clear signal from that distance – but if you take the iPod on your deck, you’ll have no problem. Other companies, such as Oregon Scientific, are working on iPod-specific speaker systems with 100-foot broadcasting distances, but they are not out yet. In the meanwhile, you could look to companies such as Recoton for wireless solutions that won’t match the iPod, but will work with it.
Another alternative is to use Apple’s AirPort Express, which allows you to stream music from any computer that’s running iTunes. However, you’ll need to have a wireless networking card in your computer, and you cannot control the music very easily: you’ll need to be in front of the computer to change songs.