ArnieZ.
Any COM DLL can be used from .NET. Adding it as reference in visual studio will generate a DLL called
"YourDll.Interop.dll"
This is a .NET -> COM marshaling library, and will do what you need.
You can also generate this from the command line using tlbimp.exe
Of course, you'll have to keep in mind that you are invoking COM components, and remember to use the .NET Marshaling API to decrease reference counts when you are done using them, otherwise you will cause memory leaks.
I've wrapped the interop implementation in another library that implements IDisposable on its objects so that cleanup is handled automatically before, but if it is a large library, this might not be worth the effort.