That class seems to be a hybrid. You specified public class IPHelper, which is halfway what you want. You should specify it as public ref class IPHelper. However even so, it will still not interface well with managed classes, because of the parameter types it receives. For instance a wchar_t is not the same as a System::String^ (managed C++ way to declare strings). Similarly a LPWSTR is also not the same as a System::String^. As a side note, it would be best for you to write some utility methods to convert between .NET System::Strings and wchar_t and other native strings that you will most likely need. This is an excellent article on MSDN on how to convert between all the various string types.
Now I don't know if you want to expose this class directly to C#, or have this class in turn wrapped by a better managed wrapper than what you have here. But anyway you do it, the Managed C++ class's methods have to take .NET types in order to be directly used in C# code.