In order to save yourself the headache of re-ranking thousands of songs, all you need to do is create five playlists: one for 5 stars, one for 4 stars, etc. Once the playlist is transferred to Mac, simply select all songs in the 5 star playlist and hit command-I to rank all songs as 5 stars. Repeat until all of your stars are filled.
I saw this on c|net.com (but can no longer find the link to give proper credit).

