Try the following code in a newly created VC++ Win32 DLL workspace.

// Test.h

extern "C"
{
// __declspec is a Microsoft specific extension.
__declspec(dllexport) int MySum(int first, int second);
}


// Test.cpp
#include "windows.h"
#include "test.h"

BOOL APIENTRY DllMain(HANDLE hModule, DWORD ul_reason_for_call, LPVOID lpReserved)
{
   switch (ul_reason_for_call)
   {
      case DLL_PROCESS_ATTACH:
      case DLL_THREAD_ATTACH:
      case DLL_THREAD_DETACH:
      case DLL_PROCESS_DETACH:
         break;
   }

   return TRUE;
}


__declspec(dllexport) int MySum(int first, int second)
{
   return first + second;   
}

I have compiled and built this from VC++ 6 SP4 and checked the exported ordinal MySum appears correctly.

Leave the type library out for now, get the DLL running.