Thank you for your reply. Apparently Panther and the new nano really do not work together. It's a pity.
During my searches I found this official compatibility chart and I think it is worth to spread the link:
http://docs.info.apple.com/article.html?artnum=60971
What can I do now? Buying Tiger on eBay could be a solution, but a 'real' license costs nearly a hundred bucks. What sells for less are installation CDs that came with some Mac. I doubt that it is 100% legal to sell them without the computer they shipped with, so I could just as well use my own Tiger install CDs to update my friend's iBook. The point is: I wanted to give an iPod, not to steal software :-)
I recommended Apple through a feedback form on their website that they should offer Tiger as a $20 option to iPod customers. How knows, maybe ...
Otherwise it will probably be the iPod shuffle. According to some forums, changing the colors did not break Panther compatibility (after all...)
Wolf