I bought a new iPod nano and had problems when plugged into the iMac. I wrote the following post on another thread but it should also be applicable here.
"Apple should tell the buyer/user on the package (or the instruction booklet) that the 3rd generation iPod nano requires Mac OS X v10.4.8 or later, and iTunes 7.4 or later (I have to do a little search to find these info on
http://www.apple.com/ipodnano/specs.html).
The best way is to use the latest version of Tiger (v10.4.??) and the latest version of iTunes. Otherwise, if the existing versions are not update enough, you plug in your new 3rd generation iPod nano, it will come up with errors. That was my experience this morning. To get the latest version of Tiger update and iTunes update, the easiest way is click on the blue Apple icon on the top left corner of the screen and choose Softeware Update. Then choose to update Tiger and iTunes, if the computer does not already have the most recent version.
Restart the computer after updates, plug in your iPod nano, there will be a Finder error message about 'an unknown disk' or something like that. Don't worry, just ignore that message. Start up iTunes and you will be asked to Restore the iPod software. Say yes and things will go smoothly from there.
Again, Apple should do better by telling the buyer/user what software is required in the package or instruction booklet. This will avoid surprise and disappointment which could happen when you plug in your brand new iPod nano and the first thing you receive is ERROR messages! Apple, get your act together for the customers! This is for your good and the good of the customers! Apple needs to listen to its customers in order to provide a genuinely good service, and not just sound bites!"