dll creation from cpp files

[NAB37]

I have some Borland C++ source files. I want to extract parts of them and use them in a C# project. I modified/recompiled one of the simple C++ .cpp files into a .dll file successfully and have been able to access its classes from my C# project. But...and there's always a butt...some of the C++ .cpp files make calls to classes in other C++ .cpp files. If I have two C++ .cpp files and one of them calls a class from the other C++ .cpp file, can I compile the two files into one .dll ? If so, I'm not having much luck doing this with Borland Builder 6, maybe you have some pointers. If it is not possible to do what I have described, what is the correct approach?