Public Declare Function SetWindowPos Lib "user32" ( _
  ByVal hwnd As Long, _
  ByVal hWndInsertAfter As Long, _
  ByVal x As Long, _
  ByVal y As Long, _
  ByVal cx As Long, _
  ByVal cy As Long, _
  ByVal wFlags As Long) As Long

Public Declare Function GetSystemMetrics Lib "user32" ( _
  ByVal nIndex As Long) As Long

Public Const HWND_TOP =  0 
Public Const HWND_TOPMOST = - 1 
Public Const SM_CXSCREEN =  0 
Public Const SM_CYSCREEN =  1 
Public Const SWP_SHOWWINDOW = &H40

Private Sub Command1_Click()
    MDIForm1.Show
End Sub

Private Sub Command2_Click()
    Dim cx As Long
    Dim cy As Long
    Dim lngRetVal As Long
    
    If MDIForm1.WindowState = vbMaximized Then
       MDIForm1.WindowState = vbNormal
    End If
    
    cx = GetSystemMetrics(SM_CXSCREEN)
    cy = GetSystemMetrics(SM_CYSCREEN)
    
    lngRetVal = SetWindowPos(MDIForm1.hwnd, HWND_TOP,  0 ,  0 , cx, cy, _
      SWP_SHOWWINDOW)

    ' Или так.
    'Move 0, 0, ScaleX(cx, vbPixels, vbTwips), _
    '  ScaleY(cy, vbPixels, vbTwips)
End Sub