When I moved my iTunes music collection from Vista to OS X, I was surprised there was no way to bring over the the ratings I had given to each track as well. This was a major suck, as the playlists I listened to the most where "Smart Playlists" that used my ratings.
I first tried to implement this as an AppleScript, which is seriously the worst programming language ever. Not only that, but if you have a decent iTunes library, AppleScript can't load it. Think about that for a second: an Apple product cannot consume the data created by another Apple product. I'm sorry, but that's just bad. Eventually I gave it a shot in Python & had a working solution in less than an hour.python import_ratings.py "iTunes Music Library.xml"