Uploading of Google Earth KML and KMZ Files

You need to alter the permitted mime types in the file
admin-functions.php (in the wp-admin subdirectory)

Discussion of mime types
http://bbs.keyhole.com/ubb/showflat.php/Cat/0/Number/307890/Main/289764

application/vnd.google-earth.kml+xml kml
application/vnd.google-earth.kmz kmz

If files do not launch from your website you will also have to add the mime types via cpanel