If you try to load your iTunes library into an XML parser, you are probably going to get an error because Apple, in their infinite wisdom, has seen fit to remove the DTD from their web server. If you try to load http://www.apple.com/DTDs/PropertyList-1.0.dtd you get a 404, Page Not Found. Um, Apple, could you please put it back?
Update: (9:50 p.m., 2007-01-02) If you add the two lines:
xmldoc.validateOnParse = false;
xmldoc.resolveExternals = false;
before loading the XML, it will ignore the missing DTD.