There are other FReepers much more qualified to offer you correct answers to your very good questions - I had best defer to them.
I was just raising the questions which came to my mind. If I recall correctly SP-2 did close a worm vulnerability?
Can the OS be re-installed? That might be your best option at this point frankly, it seems to me.
Disclaimer to all of the above, I’m on Linux most of the time.
(for exactly the reasons you describe)
That's not really an option for me - at this point. The computer is quite functional.