Leybman, I had the same problem with my default player and received the answer here.
Open iTunes and go to preferences-general. You will see "Use iTunes for Internet Music Playback". Hit the "Set" button and close the preferences. You now have iTunes set as the default player.
If you click on "Launch" in LimeWire, it will play your song in iTunes, and the song will be added to your iTunes Library.
Also, if you open your LimeWire shared folder, and drag a song to your iTunes library, the song will be added to the library. The file itself will still remain in your LimeWire shared folder on your hard drive.
If you copy the songs to your iTunes folder first, then drag to the library, all of your music will be stored together in one folder.
Hope this helps. I'm afraid if I say any more, I'll confuse all of us.