A. When Service Pack 4 is installed or uninstalled an Event is written to the System Event Log. The Event ID is 4353 so you could just create a filter (View - Filter Events) to view only Event ID 4353. It gives information of the person and time it was actioned.
The messages are
Windows NT Service Pack 4 was installed (Service Pack 3 was previously installed).
Windows NT Service Pack 4 was uninstalled. Restoring Windows NT to Service Pack 3.