iPod problem - iTunes are deleting my playlists

Are you using the same iTunes Library (and the same laptop) that you used to add the music originally?

Also, have you had the laptop repaired or have you reinstalled iTunes since you originally added the music to it?

Possibly, although I'm not sure what else you have done.

If you select Manually Manage, then any changes on your iPod would never be copied back to your iTunes Library, so neither the playlist on your iPod nor the copy in your library should be affected.

Back to reinstalling iTunes:

if you reinstall iTunes and then try to synchronise (Sync) with the iPod, iTunes would almost certainly see the content on the iPod as coming from a different library and would give you a message stating that if you proceed with a Sync, all the existing content would be removed from the ipod. Did you see any such message?