Synthfreek:
You should backup everything in your iTunes folder and not just the actual music files.
Good advice, but ....
On a Windows box, if you have your iTunes directory set to somewhere other than the default, as I do (E:\iTunes) then the music files are there, but the two files that represent the database are not.
They remain in My Documents\My Music\iTunes.
The two files are iTunes Music Library.xml and iTunes Library.itl. You should back these up but you do have options. If all you have is the .xml file, iTunes can rebuild the .itl database file.
If you have neither (have lost them due to a crash) you can rebuild by adding the folder containing the music to the library, but this is sometimes not possible, and you have to add the files - that's super painful, but does work. If it is possible, it will take a long time for iTunes to crunch its way through.
If you have downloaded artwork from iTunes Store you also should have a backup of "Album Artwork".
So when you make a backup of your music files on a PC, copy the My Documents\My Music\iTunes folder that goes with it at the same time.
It's possible that the backup utility inside iTunes does both for you - never tried it. I have experienced corruption of the iTunes DB so I am pretty careful now.
Regards,
