apparently this works but i haven't tried it personally
1. Connect the iPod to your PC. If iTunes starts syncing (ie erasing) your music automatically, hit the X in the upper right hand corner of iTunes display, to the left of the search box, to stop it.
2. In Control Panel, Portable Media Devices, double-click your iPod.
3. In the Tools menu -> Options, in the View Tab, check "Show hidden files and folders."
4. Navigate to the Music folder. On my 2nd gen 'pod, the full path is
Portable Media Devices\GINA'S IPOD (F:)\iPod_Control\Music
5. Select all the music folders, and drag and drop them into a folder on your hard drive, or directly into iTunes.