I just tried it out with BearShare 5.1b (which was connecting to 20 UP's.) I discovered if I simply drag & dropped a fresh audio file into my BearShare download folder, within a short time iTunes would open & copy it to its own music library. I think it depends on your settings in both Bearshare & iTunes.

That audio file I tried out was not previously in the iTunes music library. (It was a recently downloaded rare concert song via torrents; the band's re-union concert for a special appeal, no recording ever officially released. I would have bought it otherwise since I'm a hardened fan of theirs.)