2. About the XML file

The XML file resides in your home directory, at ~/Music/iTunes/iTunes Music Library.xml. It has been described as braindead and, agreed, it does not look like one would expect an xml file for a music library would look like. It is track based, and every track has an ID and most of the information one would expect to find there, except for some, like the images. There does not seem to be a logical way in which the Track IDs are assigned and they tend to change when f.i. you reencode songs. Where one would expect the name of the tag has information about the information contained in the tag, the XML file just has key tags followed by value tags, like a dictionary streamed out. This is the typical plist approach of Apple, and it's just another example of how not to use XML, imho.

When you are playing tracks in your iTunes application, iTunes seems to update both a private proprietary database file and the xml file. The proprietary database, ~/Music/iTunes/iTunes 4 Music Library, is the master file. Whatever you change in the xml file, if the database file is not updated, the next time you play something in iTunes, the XML file will be updated again. Very annoying.