Ok, I'm really annoyed with Microsoft now.
Granted, this all started out with a stupid mistake on my part -- but now it turns out that to fix that mistake, I have to _completely reinstall a machine!_
Here's what happened...
I was working on an XP Pro box and was wondering if the problems that my user was having with her anti-virus not updating properly (she's a "limited user" on the machine -- no admin rights) were because of NTFS permissions issues. So I went about using the
cacls command to change the permissions in the anti-virus software directory (yes, I know this isn't a Good Idea -- but I wanted to see if it would work; I wanted to see if NTFS permissions were the issue). Well, I borked up the syntax of the cacls command, and ended up erasing all the perms out of c:\windows (and apparently some of the subdirectories). Doh! Stupid, stupid, stupid...
But the problem gets worse. Going to another machine, I notice that there are complicated permissions on c:\windows (and friends). So I look up the help page (and "http://support.microsoft.com/":http://support.microsoft.com/), and notice that cacls _cannot set these permissions!_ That's right: you can use cacls to bork up the permissions on your machine, but you _cannot_ use it to fix them!
That is unbelieveable to me. I could not find any GUI method of changing the permissions, either. Hence, I'm going to have to fully re-install the box to really fix the problem. Totally, totally lame.