Well, just remember what the user has entered, and if the cheat code is in the text they've entered, then show the label.
Once the cheat code has been entered, you'd want to clear the buffer so that the label can be shown again at a later stage.

Dim entered as string
Private Sub Form_KeyPress(KeyAscii As Integer)
entered = entered & Chr(KeyAscii)
If (InStr(1, entered, "0513", vbTextCompare) <> 0) Then
entered = ""
Label1.visible = true
End If
End Sub