iTunes Library Updater
ITLU allows you to scan a Windows system for mp3s and add them to your iTunes library, regardless of the source. Most importantly, it allows you to update your existing library, which iTunes doesn’t allow. You’ll need this app and a pile of mp3s, whether they’re on your computer’s hard drive or on an external drive [even on an external system]. You can have ITLU scan your whole system for mp3s and add them to iTunes, or point it at a specific place.