Solution – Galaxy Drums is a large download. It is split into an archive. On OSX you must use http://www.kekaosx.com to extract the downloads and on Windows you must use http://www.7-zip.org/download.html
Use of any other unzipping tool is not supported and will most likely say that it can not be unzipped or that the download is corrupt.
Make sure all downloads of the Galaxy Drums content are placed into the same folder before attempting to extract/unzip, then right click on Galaxy Drums Installer 001 and choose 7zip (or Keka) and extract. This will unzip all 7 parts into a single installer folder.