HDC hdc = BeginPaint( hWnd, &ps )
HDC MemDC = CreateCompatibleDC( hdc )
HDC BGMemDC = CrateCompatibleDC( hdc )
HBITMAP bgBuffer = CreateCompatibleBitmap( hdc, x, y )
HBITMAP Old = (HBITMAP) SelectObject( BGMemDC, bgBuffer )
HBITMAP Old2 = (HBITMAP) SelectObject( MemDC, bmp )
BitBlt( MemDC to BGMemDC )
SelectObject( MemDC, Old2 )
BitBlt( BGMemDC to hdc )
SelectObject( BGMemDC, Old )
DeleteObject( MemDC )
EndPaint( hWnd, &ps )