OpenGL1.2 SDK

Hello, could anyone tell me how to buy the OpenGL
1.2 SDK (C++ Version)?

Not sure what you mean. If you are an application developer and want to use OpenGL, its free and you dont have to buy anything. Only if you plan to write your own OpenGL implementation you need a licence

The header and lib files usually come with your compiler i.e. Visual Studio or gcc or whatever.

The only drawback: The Windows libraries only supports OpenGL up to version 1.1 and version 1.2++ functioniality is only provided thru the extension mechanism.