What do you mean compressed to 12sky2?
All you have to do is extract it using WinRar to a random directory, lets say the desktop
Then open the folder then open MapFun
If you did that, then like said try redownloading .NET Framework 3.5
Also Run as administrator on Vista or 7 and if that doesnt work turn off User account control
If that doesnt work then please post a screen of the error you are getting
EDIT: Didnt see that you had posted already megabyte...lol well 2 people helping is better than one i guess lol