iTunes Library Updater is described as 'As iTunes doesn’t provide a function to update / synchronize your music collection with it’s own database, I’ve written a small utility for that purpose'. There are three alternatives to iTunes Library Updater for Windows. The best alternative is iTunes Library Toolkit. It's not free, so if you're looking for a free alternative, you could try iTunes Folder Watch or iWatchSyncer.
The iTunes Library Toolkit will greatly simplify the ongoing maintenance of your iTunes library. The following functions are part of the toolkit: New Media - detects new media under watched folders and adds them to iTunes.