I successfully updated my Vista system to v. 8.0.059 today, but only after trying to do it since last Tuesday. The villain turned out to be F-Prot, but I discovered this after completely removing ZoneAlarm (using your recipe, gleaned from my wife's computer) and following your tip that this particular update was not very AV friendly.
I have used ZoneAlarm Pro for eight years and had no previous difficulty with updates, though I have never had to switch off F-Prot. Perhaps you should warn users before inviting them to update. It would save a lot of tears.