Songbird is not working right on my machine, i'm trying to recover my playlists...
According to the Satisfaction site of Songbird, playlists are stored in an internal database.
Thus they are only accessible via Songbird...
You can export playlists from songbird as .m3u files using the following addon: http://addons.songbirdnest.com/addon/51
Then you can use an alternative player such as MediaMonkey to scan the .m3u files and it'll recreate the playlist within its library.
Disclosure: I work on MediaMonkey