I still get this alot about why some skins come down as .ZIP instead of .WBA so I decided to be of a little assistance.
If using Internet Explorer you should Change the file-extension from .ZIP to .WBA, but FIRST You have to go to -
Controlpanel / FolderOptions / View-tab and uncheck "Hide extensions for known file types" -checkbox.
THEN you will see the extensions such as Zip, Rar, Wba etc and then you can change the files name from .ZIP to .WBA
An alternative way is to use FireFox instead of InternetExplorer. For some reason it comes down as WBA then...
Hope this helps you when searched the forum for answers.