Your ipod is register in iMac can you still use itunes that are on windows?
If you have synced your iPod with your iMac, you will still be
able to use iTunes on your Windows computer, though if you want to
sync your iPod with your Windows computer, you will need to
reformat the iPod to work with the Windows platform. This means
everything on your iPod will be deleted. You can only use your iPod
with one operating system at a time.