Use a C# DLL from a VC++ 6 application

I have a large code base written in VC++ 6 that I would like to migrate to C#.  I am thinking that the best way to do this is to implement pieces of the code in C# and call them from the C++ program.

I am trying to figure out how to write a C# DLL that can be called from a C++ 6 application.  There are plenty of examples out there describing a console DLL that does this but I need to be able to have a user interface for the C# piece.

Does anyone know how to write a C# DLL that uses MFC or Windows UI that can be called from a VC++ 6 application?