Option Explicit

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 SetWindowsHookEx Lib "user32" _
      Alias "SetWindowsHookExA" (ByVal idHook As Long, _
      ByVal lpfn As Long, ByVal hmod As Long, ByVal _
      dwThreadId As Long) As Long

Public Declare Function UnhookWindowsHookEx Lib "user32" _
      (ByVal hHook As Long) As Long

Public Declare Function GetCurrentThreadId Lib "kernel32" () _
      As Long

Public Const SWP_NOSIZE = &H1
Public Const SWP_NOZORDER = &H4
Public Const SWP_NOACTIVATE = &H10
Public Const HCBT_ACTIVATE = 5
Public Const WH_CBT = 5

Public hHook As Long
Public posX As Long
Public posY As Long

Public Function WinProc(ByVal lMsg As Long, ByVal wParam _
      As Long, ByVal lParam As Long) As Long
  If lMsg = HCBT_ACTIVATE Then
    SetWindowPos wParam, 0, posX, posY, 0, 0, SWP_NOSIZE Or _
       SWP_NOZORDER Or SWP_NOACTIVATE
    UnhookWindowsHookEx hHook
  End If
  WinProc = False
End Function

Option Explicit

Private Sub Form_Load()
  txtPosX = 0
  txtPosY = 0
End Sub

Private Sub Command1_Click()
  Dim hInst As Long, Thread As Long
  Dim msg As String

  If Check1.Value = 1 Then
    msg$ = "Die MessageBox ist jetzt zentriert."
  Else
    hInst = App.hInstance
    Thread = GetCurrentThreadId()
    hHook = SetWindowsHookEx(WH_CBT, AddressOf WinProc, _
        hInst, Thread)
    posX = CLng(txtPosX)
    posY = CLng(txtPosY)
    msg$ = "Die Position der MessageBox ist an:" & _
        vbCrLf & vbCrLf & "X-Position: " & posX & vbCrLf & _
        "Y-Position: " & posY
  End If

  MsgBox msg$, vbOKOnly + vbInformation, _
          "Position der MessageBox", 0, 0
End Sub