I asked aloud: "Can I just modify boot.ini?".
As I started researching that, I decided to have a look at my current boot.ini. Well, it turns out I have no boot.ini! I can find it neither by looking (with view hidden and system files turned on), nor by searching, nor through EasyBCD, which complains that it can't find boot.ini either.
Now, I've only recently switched over from XP to Vista, so maybe there's something I'm missing, but as I understand it I should not be able to boot up at all without this file.
And yet, here I am... How can that be accounted for?
(And by the way, I've scanned my entire system for viruses and malware with several different apps).