This (Windows only) script will scan your iTunes music library and create playlist folders and playlists that reflect the directory structure on disk.
If you tell iTunes not to copy your music but leave it in its original location, this lets you create a custom hierarical organization for your music that iTunes does not appear to otherwise support.
The default library location is "C:\Music", edit the script as needed.
The script is run using the Windows program "wscript". It has been very lightly tested on Windows 2000 and Windows XP, but the usual caveats apply.
Windows JScript iTunes Playlist Builder