One of the weakness of iTunes (at least up to version 8) is the "missing" capability to monitor media files being added or removed from a folder.  This may be a design decision on the part of Apple to lock user down to use iTunes for media file library management. For people who are managing media files manually or uses multiple media file management software like Windows Media Player, the "missing" capability in iTunes causes great inconvenience.  Windows Media Player has this feature working very nicely.  There is no option other than to use external program to plug the hole in iTunes.  The iTunes Library Updater is one nice simple uility written for this purpose.  It has to be run separately from iTunes, either as a Windows application or command-line application.