iPod in Rental Car?

It should be fine....most of these mini-transmitters offer three or four different frequencies you can switch between, so you should be OK in Europe, although be aware that in some urban areas, their FM band is VERY crowded with stations.

I am also planning on doing this, so I can't see it being a problem :)

Beats carrying around cds :)

I did the same thing in Ireland last year and it worked very well. I'm pretty sure Germany will be fine too.

I was recently in Ireland, and we had a rental car--a Hyundai. We used an iPod hook-up like the one you're talking about for a while, but our car, which seemed pretty new, actually had a (bear with me, I might be using the wrong terminology) USB port in it. I plugged in the cord I usually use to upload songs onto my iPod from the computer, and it instantly started playing songs. It was nice, because then you're not using up the battery charge. However, it was kind of annoying, because it kept starting at the beginning of some list I didn't set up myself. Each time we plugged it in, it was the same thing.

Thanks Everyone!