I think you can but i find you need to be careful. You can experiment by deleting a song you don't want and see if it also deletes it off the ipod next time you plug it in. Failing that back up your songs to cd. You can get about 120 songs I think on one cd in mp4 format but I think it will only play on a computer.
I've managed to delete my ipod before somehow -still not sure how- but usually leave it on on the computer as I only have 2gb nano ipod and I change the music alot.
Thinking about again after i have loaded the ipod in the music section of the ipod on the computer I uncheck the boxes so that when i plug it in next time it doesn't automatically sync the ipod. Hope that helps but experiment first with something that doesnt matter! Sometimes there is a glitch and its best to restore the settings. Good luck.