Option Explicit
Private Declare Function GetWindowsDirectory Lib "kernel32" Alias _
  "GetWindowsDirectoryA" ( _
ByVal lpBuffer As String, ByVal nSize As Long) As Long
 
Private Sub Form_Load()
   MsgBox GetWinDir
End Sub
 
Function GetWinDir() As String
Dim nAs Long
GetWinDir = String(100, vbNullChar)
n= GetWindowsDirectory(GetWinDir, 100)
If n <> 0 Then GetWinDir = Left(GetWinDir, n)
End Function