Are you using your iPod also for data or just music? If you have a "partition" inside it to store your data files besides your music, then something is wrong (or you have an option checked in your iTunes that doesn't allow Device Manager to see it - I forgot which option was it). If you have it ONLY for music (without the mass storage optin enabled), then it's ok. You cannot use your Windows Explorer to get music in your iPod... for that you use iTunes.