In ITunes preferences, advanced pane, make sure you "keep iTunes
folder organized. Open up a terminal window and type
defaults write com.apple.finder AppleShowAllFiles TRUE
then relaunch the finder.
You'll see that you can see all sorts of files now. Go to your hard drive and maneuver to Volumes, then your ipod, then iPod_Control, then Music. You'll se a list of folders from F00 to Fxx.
Open Itunes; go to each of the Fxx folders, select all songs, and drag and drop them to the ipod library.
If you want to no longer see all the annoying files, go back to terminal
and type
defaults write com.apple.finder AppleShowAllFiles FALSE
Note that this won't let you pick what songs to import; the songs are shown on the ipod in some weird hash filename which makes no sense.
I've also ran across some programs that do the same thing, and some interesting website to tell you about it. For the PC there seems to be a program called "ephpod". Here are some interesting links: