Tienes que usar el API de windows, no recuerdo haberlo probado en W2000, pero en 98 si funcionaba.
Private Declare Function SystemParametersInfo Lib "user32" Alias "SystemParametersInfoA" (ByVal uAction As Long, ByVal uParam As Long, lpvParam As Any, ByVal fuWinIni As Long) As Long
Private Const SPI_SCREENSAVERRUNNING = 97&
Private Sub DesHabilitar_Click()
Dim lngRet As Long
Dim blnOld As Boolean
lngRet = SystemParametersInfo(SPI_SCREENSAVERRUNNING, True, blnOld, 0&)
End Sub
Private Sub Habilitar_Click()
Dim lngRet As Long
Dim blnOld As Boolean
lngRet = SystemParametersInfo(SPI_SCREENSAVERRUNNING, False, blnOld, 0&)
End Sub