
If you want to share a common set of music and video among multiple users, but still allow each user to maintain their own library with separate playlists, ratings, etc., you can use PowerTunes to do so. To share a media folder, first select a library that is using the media folder that you'd like to share, then select "Share Media Folder" from the Library menu. You will be presented the same options as when sharing a library, but these options will only be applied to the media folder, and the selected library will remain unshared.
Once you have shared a media folder, there are two ways for another user to use that media folder with one of their iTunes libraries.