Option Explicit
 
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 Const SWP_NOSIZE = &H1
Public Const SWP_NOMOVE = &H2
Public Const FLAGS As Long = SWP_NOMOVE Or SWP_NOSIZE
Public Const HWND_TOPMOST = -1
Public Const HWND_NOTOPMOST = -2

Private Sub chVordergrund_Click()
  If chVordergrund.Value = vbChecked Then
    SetWindowPos frmStart.hWnd, HWND_TOPMOST, 0, 0, 0, 0, FLAGS
    SetWindowPos Me.hWnd, HWND_TOPMOST, 0, 0, 0, 0, FLAGS
    SetWindowPos frmUeber.hWnd, HWND_TOPMOST, 0, 0, 0, 0, FLAGS
    SetWindowPos frmKontaktliste.hWnd, HWND_TOPMOST, 0, 0, 0, 0, FLAGS
 
  Else
    SetWindowPos frmStart.hWnd, HWND_NOTOPMOST, 0, 0, 0, 0, FLAGS
    SetWindowPos Me.hWnd, HWND_NOTOPMOST, 0, 0, 0, 0, FLAGS
    SetWindowPos frmUeber.hWnd, HWND_NOTOPMOST, 0, 0, 0, 0, FLAGS
    SetWindowPos frmKontaktliste.hWnd, HWND_NOTOPMOST, 0, 0, 0, 0, FLAGS
  End If
End Sub