Private Declare Function SendMessage Lib "user32" Alias _
  "SendMessageA" _
  (ByVal hWnd As Long, _
   ByVal wMsg As Long, _
   ByVal wParam As Long, _
   ByVal lParam As Long) As Long
 
Private Const EM_GETLINECOUNT = &HBA
 
' Beispiel: Max. 3 Zeilen
Private Const MAXLINE = 3
 
Private Sub Text1_KeyPress(KeyAscii As Integer)
  Dim rVal As Long
 
  ' Anzahl Zeilen ermitteln und prüfen
  rVal = SendMessage(Text1.hWnd, EM_GETLINECOUNT, -1, 0&)
 
  If KeyAscii = 13 Then
    If rVal >= MAXLINE Then KeyAscii = 0
  Else
    If rVal > MAXLINE Then KeyAscii = 0
  End If
End Sub