let me try to clarify what i explained above, hope it helps...

in limewire prefs., i changed the default share folder to my "itunes music" (which is the library where itunes music is stored), i don't use the "shared" users folder which is the limewire default...
i also deselect "use limewire player".

with this setup, i don't get the "add to library" message, because the download is put into the library by limewire and is automatically available to itunes...

by doing this, when i import a cd into itunes, it then automatically becomes shared in limewire!