Perhaps everyone else has already figured this out. You can't easily get music onto an iPod, but you can get it off. And, at least in Windows XP, it's pretty straight forward.
Go to the iPod_Control folder on the iPod and then do a search in Music for *.mp3 *.m4p etc. You can add Artist and Album to the columns of a search results. If you sort by those fields you can copy just the stuff you want. Move the files somewhere and then import them into iTunes. The ID3 tags should mean it doesn't matter that the files have weird code names. If you have iTunes managing your songs it will rename them for you.