i would suggest Linux rather than Window for Blackhat Activities ... ( BACKTRACK ) is One of my Favorite
OS seriously does not matter.
I think you can use any type of OS for Blackhat things But windows 2008 is very good for this type of things.
I dont think its the key. If you know the basics you can handle anything just need some basic
There's only one OS important in Blackhat and that's OldSalt
For the rest: it depends on what you're planning to do.
For Data mining which OS is best ?