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
Const SPI_SETSCREENSAVEACTIVE = 17
Private Sub DesHabilitar_Click()
    Dim lngRet As Long
    lngRet = SystemParametersInfo(SPI_SETSCREENSAVEACTIVE, True, 0, 0)
End Sub

Private Sub Habilitar_Click()
    Dim lngRet As Long
    lngRet = SystemParametersInfo(SPI_SETSCREENSAVEACTIVE, False, 0, 0)
End Sub