I discovered this by accident. Spotlight will index your iPod, but not your music files. But using the Terminal, you can force it to index music with the following command:
sudo mdimport -f /Volumes/your_iPod/iPod_control/
After you have indexed your iPod music, search for your music and view it in the Spotlight window. Double-click on a track of your choice and it will be imported into your iTunes music library and copied to your Mac's iTunes Music folder.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050501183645647