According to wikipedia, kmz is a:
DescriptionKeyhole Markup Language is an XML notation for expressing geographic annotation and visualization within Internet-based, two-dimensional maps and three-dimensional Earth browsers. KML was developed for use with Google Earth, which was originally named Keyhole Earth Viewer.
However, the KMZ file got exported by Google Earth is not a XML one. It's even not a XML file but a binary file.
How can I see the XML content?