Option Explicit

Private Declare Function GetWindowsDirectory Lib "kernel32" _
    Alias "GetWindowsDirectoryA" (ByVal lpBuffer As String, _
    ByVal nSize As Long) As Long

Function GetWinDir() As String
  Dim strDir As String
  Dim nLen   As Long

  strDir = Space(255)
  nLen = GetWindowsDirectory(strDir, 255)
  strDir = Left(strDir, nLen)

  If Right$(strDir, 1) <> "\" Then strDir = strDir & "\"

  GetWinDir = strDir
End Function

MsgBox "Windows-Verzeichnis: " & GetWinDir