Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal _
  hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal _
lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal _
hWnd1 As Long, ByVal hWnd2 As Long, ByVal lpsz1 As String, ByVal lpsz2 As _
String) As Long
 
Const WM_SetText = &HC
 
Private Sub Command1_Click()
Dim hwndWin As Long
Dim hwndText As Long
 
  hwndWin = FindWindow(vbNullString, "test") ' hier den Fenstertitel ändern
  hwndText = FindWindowEx(hwndWin, 0&, "ThunderTextBox", vbNullString) ' hier
  ' die Klasse ändern die in Spy++ stand.
 
  Dim t As String
  t = "Hallo das ist ein Test"
  SendMessage hwndText, WM_SetText, 0&, ByVal t
End Sub