The thing would not download updates. It would just say "Downloading updates..." and stall for hours at a time. I searched as much as I could online and only found barely any help. Most of it involved stopping the windows update agent service, and then deleting cached update files. But then it would just freeze again when I started it again. After a whole bunch of attempts, I noticed it was filling up the cache folder again after every time I restarted the update service, and that if I waited a bit, and then rebooted the computer, it would apply a few patches.
I've seen several XP sytems do something very similar, but it kept processor usage around 90%-100% the whole time it was downloading. The hotfix that was supposed to fix the issue was useless, all you could really do was not use the PC while it was updating. After a certain point / update this behavior would stop. Was never sure which update fixed it because I didn't have time do one update at a time.