C++ data types into C# datatypes

Question

I know these aren't correct, but I'm stumped as to how I should go about importing 2 functions I compiled into a dll from a post from www.ring3circus.com; into a C# application. I've never tried importing functions from a non-C# dll before, so I've been googleing all day but to no avail.

In C# app:

[DllImport("R_3D_BYOND.dll", CharSet = CharSet.None)]

public static extern int Initialise(int h);

[DllImport("R_3D_BYOND.dll", CharSet = CharSet.None)]

public static extern int Release(/*What parameter do I use? Null?*/); //what's the equivalent of a DWORD in c#? is this where I MarshalAs something?

In C++ dll:

DWORD WINAPI Initialise(__in LPVOID lpParameter)

DWORD WINAPI Release(void* parameter)

The overall project I'm working on is a little wild because it incorporates 3 overall languages, but the resulting effect would be neat, so I'd appreciate any help I can get.