' benötigte API-Deklarationen
Private Declare Function SetWindowLong Lib "user32" _
  Alias "SetWindowLongA" ( _
  ByVal hwnd As Long, _
  ByVal nIndex As Long, _
  ByVal dwNewLong As Long) As Long
 
Private Declare Function SetParent Lib "user32" ( _
  ByVal hWndChild As Long, _
  ByVal hWndNewParent As Long) As Long
 
Private Declare Function GetWindowLong Lib "user32" _
  Alias "GetWindowLongA" ( _
  ByVal hwnd As Long, _
  ByVal nIndex As Long) As Long
 
Private Declare Function GetParent Lib "user32" _
  Alias "GetParent" ( _
  ByVal hwnd As Long) As Long
 
Private Const WS_EX_MDICHILD = &H40&
Private Const WS_EX_WINDOWEDGE = &H100&
Private Const GWL_EXSTYLE = (-20)
 
Private nOldStyle As Long
Private nOldParent As Long
 
' beliebiges Fenster als Child-Form im MDI-Formular anzeigen
Public Sub MakeChild(ByVal hWndChild As Long, ByVal hWndMDI As Long)
  ' zunächst den Original-Fensterstil und Parent merken
  nOldStyle = GetWindowLong(hWndChild, GWL_EXSTYLE)
  nOldParent = GetParent(hWndChild)
 
  ' jetzt das Fenster zum ChildForm der MDIForm machen
  SetParent hWndChild, hWndMDI
  SetWindowLong hWndChild, GWL_EXSTYLE, WS_EX_MDICHILD Or WS_EX_WINDOWEDGE
End Sub

mfg Lukas