There's been at least 10 threads on this. The answer is also just a quick Google away.
Anyway, Plug in ipod -> Go to my computer -> open the ipod as a mass storage device -> unhide all files
A folder should be unhidden that contains all of your songs in some stupid encrypted language. Don't worry they'll be back to normal when you put them back in to itunes.
You should have backed up your music in the first place though.