Here you go:

Private Declare Function SystemParametersInfo Lib "user32" Alias _
"SystemParametersInfoA" (ByVal uAction As Long, ByVal uParam As Long, _
ByVal lpvParam As Any, ByVal fuWinIni As Long) As Long


Private Sub DisableCtrlAltDelete(bDisabled As Boolean)
Dim x As Long
x = SystemParametersInfo(97, bDisabled, CStr(1), 0)
End Sub

Private Sub Command2_Click()
'Enable CtrlAltDelete
DisableCtrlAltDelete (False)
End Sub

Private Sub Command1_Click()
'Disable CtrlAltDelete
DisableCtrlAltDelete (True)
End Sub