Non Square Window Shapes

I have a program somebody gave me that creates an non-square window.  Has anybody else seen this?  What I need to know is if there is some way to do this for a Dialog box instead of a SDI.  Here is the code for SDI:

#include <windows.h>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
            PSTR szCmdLine, int iCmdShow)
{
      static char szAppName[] = "App Name";
      static char szAppTitle[] = "App Name";
      HWND hwnd;
      MSG msg;
      WNDCLASSEX wndclass;

      wndclass.cbSize = sizeof(wndclass);
      wndclass.style = CS_HREDRAW | CS_VREDRAW;
      wndclass.lpfnWndProc = WndProc;
      wndclass.cbClsExtra = 0;
      wndclass.cbWndExtra = 0;
      wndclass.hInstance = hInstance;
      wndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
      wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
      wndclass.hbrBackground = (HBRUSH) GetStockObject(WHITE_BRUSH);
      wndclass.lpszMenuName = NULL;
      wndclass.lpszClassName = szAppName;
      wndclass.hIconSm = LoadIcon(NULL, IDI_APPLICATION);

      RegisterClassEx(&wndclass);
      hwnd = CreateWindow (szAppName, szAppTitle,WS_OVERLAPPEDWINDOW,
            CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
            NULL, NULL, hInstance, NULL);
      ShowWindow(hwnd, iCmdShow);
      UpdateWindow(hwnd);

      while (GetMessage (&msg, NULL, 0, 0))
      {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
      }
      return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
{
      HDC hdc;
      PAINTSTRUCT ps;
      RECT rect;
      HRGN Rgn;
      POINT points[5];
      int AutoMagic = -1;

      switch (iMsg)
      {
            case WM_CREATE :
                  SetWindowRgn(hwnd,NULL,FALSE);
                  GetWindowRect(hwnd,&rect);
                  points[0].x = points[0].y = points[1].x = 0;
                  points[1].y = GetSystemMetrics(SM_CYMENU) + GetSystemMetrics(SM_CYCAPTION);
                  points[3].x = points[4].x = rect.right - rect.left;
                  points[4].y = 0;
                  points[3].y = points[1].y;
                  points[2].x = (rect.right - rect.left)/2;
                  points[2].y = rect.bottom - rect.top;
                  Rgn = CreatePolygonRgn(points,5,WINDING);
                  SetWindowRgn(hwnd,Rgn,TRUE);
                  return 0;
            case WM_PAINT :
                  hdc = BeginPaint(hwnd, &ps);
                  GetClientRect(hwnd,&rect);
                  DrawText(hdc, "Inside the Window!", AutoMagic, &rect,
                        DT_SINGLELINE | DT_CENTER | DT_VCENTER);
                  EndPaint(hwnd, &ps);
                  return 0;
            case WM_DESTROY :
                  PostQuitMessage(0);
                  return 0;
      }
      return DefWindowProc(hwnd, iMsg, wParam, lParam);
}


This is pretty clever programming, but is it possible for Dialog boxes and can I implement it in C++ using MSVC++5.0?