The following explanation assumes you know your way round the above two music players.
Here are the steps
- Go to ‘Rated’ in WMP and select My Rating 4 star say. Select all. Add to the playlist. Name the playlist 4star (or whatever you choose) and choose save as an M3U file.
- Go to iTunes. Go to Library > Import playlist. Import the 4star.m3u playlist. Select all the tracks. Right click and choose 4 star rating. Then all of those tracks will be set to 4 stars.
- Repeat for the other ratings