Since my tragedy the other day I’ve been pretty busy working on things. My laptop was fine after the reboot, but the desktop was badly broken. It would start up just fine but once it started Explorer (the desktop, start bar, etc) would restart once every 3 seconds or so. I finally got it working, so I thought I would outline my steps here for the sake of anyone else who may have had a similar problem.

1. First I wanted to stop the explorer restarts and so I hit ctrl+alt+delete and went to the task manager. Then I played a game of computer whack-a-mole. If you click on the constantly respawning explorer.exe task and end the process before it kills itself, it’ll stop restarting. Luckily my desktop isn’t too fast so I was able to catch it.
2. At this point I decided that something must have gone wrong with the update, possible because the computer was on an old version of XP (SP1 or earlier) so the best remedy would probably be updating again. Unfortunately Internet Explorer wouldn’t run. I was able to start up Firefox through the task manager by going File > New task (Run...) and navigating to Firefox.exe on my hard drive but though it ran You can’t use Windows Update on Firefox, so I was still out of luck.
3. While in the Run file dialog I noticed that my Samba network shares were mounted, so I could get files onto the desktop that way.
4. I happened to have a copy of the downloadable Service Pack 2 file (270 MB) from Microsoft that’s much better than the network install thing. I honestly don’t remember what hoops I jumped through on their download site to get this or I would point you there. It’s a great thing to have on a CD.
5. I copied that file to the Linux server and then using the Run dialog to open it from the mapped network drive on the desktop.
6. I used task manager to shut down everything non-essential that was running in the background.
7. The service pack installer ran. It came down to the reboot time and I crossed my fingers. When Windows finally restarted everything worked fine again.

There was probably a better way to do this, but this is just the path I took.

Also see these instructions for disabling automatic reboots but leaving automatic updating.