I downloaded the OS X VirtualBox images and had some trouble unzipping with the default Archive Utility app (it would produce an unusable .cpgz), so I downloaded an app called The Unarchiver from the App Store and used that to unzip them, I'm sure there's some others that would work too. That app worked as intended and produced a .ova file. Then all that's needed when you open VirtualBox is choose File &gt; Import Appliance... pick your .ova and it should be ready to go after it loads up.