Mixing C++ and C# - References, Examples

Question

I have a C++ application that contains some graphics. I would like to use this application with a C# applicaton and have the applications communicate with each other. My thought is to modify the C++ application by adding some access Methods and use it within the context of a UserControl. My other thought is to strip the Main portion ot the C++ applicatioin and place the Classes into a dll to use within the C# application. I believe that either of these will work, but I dont know where to start. Does anyone know of references or examples that might help get me started? Thanks in advance.