I think this might have been a bug in that version of LW (5.1). The most recent version is LW 5.5.13 so not sure you wish to update. Download LimeWire 5.5.13 - Lime Wire
The system of sharing back in that version is a little different to now, it's much more straight forward. LW 5.1 used what might be called 'watch' or 'monitor' folders, if any new files were added to those folders they would be added to share, or library at least (I can't recall which.)