I'm not sure I was entirely clear in my second post.
Originally, I used a line in my code like this
ZipFile zf = new ZipFile(@"Data\MyPlaces.kmz");
After I read the link that I referenced above, I made a copy of MyPlaces.kmz and renamed the copy to "MyPlaces.zip". Then in my code I switched the line to
ZipFile zf = new ZipFile(@"Data\MyPlaces.zip");
and I was able to access the contents of the file.
I'm not sure why Google felt the need to create a new extension for a common file compression format. It seems to indicate that I have do a file copy and rename before I unzip the file in my program.