I agree with earlier posts that discourage the FM modulator. My wife uses i-Trip w/ her iPod Mini when driving her Pacifica. Now, she enjoys her iPod, but when she rides with me in the X, we notice a dramatic difference in the sound quality using my combination of the Aux input w/ the Belkin cable.

At first, I connected my iPod to the Aux input using the headphone jack. If I remember correctly, the volume adjustment required both adjusting the volume on the iPod AND the volume on the BMW stereo. Also, the sound seemed low (but this may because I didn't find the right balance between the two units). However, the Belkin cable connects to the iPod dock connector to charge the iPod and to provide a line out. Now I connect using the line out on the Belkin cable to the Auxiliary input (I need to do a better job hiding my cables, though). Now, the only volume I adjust are the steering wheel controls and I think there is a huge improvement in overall sound quality.

Oh yeah, I usually leave my 20GB iPod on shuffle. With 4800 songs, I'm enjoy hearing songs I haven't heard in a long time.