I think I figured out how to import mp3s from Limewire to OSX ITunes:
in ITunes, go to File -- Add to Library. In the list on the left where you can choose where to import from, click on "Shared". Highlight the songs you want to import (hold down the shift key and click if you want to highlight more than one at once) then click "Choose". Hopefully, the Limewire mp3s will show up in your ITunes library.