I recently switched my wife's laptop from running Vista to Win7. The old OS had iTunes installed, all tracks volume matched, album artwork found, playlists created and tags updated. All media is on a NAS drive, but her "iTunes folder location" was in her Music documents folder. I copied that folder to a location on the Win7 drive, but the library isn't restored.
I'm not certain I'm going about this in entirely the wrong way. All the guides I see are for moving all the media, which is in the same place (the NAS drive). All I want is to have the old setup of playlists, artwork, tags and volumes without having to do it again. It's easily my #1 gripe about iTunes.
Was the folder location on the Music folder or the Music Library? You can setup the Music Library to go to different folders, including that NAS, was that setup at some point?
Did you do an export of the library from iTunes before the OS migration? The playlists are stored inside the database, if you did not export them, they are in the database that was created on the old OS, no longer exists on the new setup.
Did you do this http://support.apple.com/kb/HT1382 or just tried to copy the folders? If you just copied the folders, you will have issues. What you did not do is copy the database files that iTunes created linking the art to the songs and the playlist files.