My XP Pro does updates in the background because I allow it to. Its SP2 but I believe SP1 does the same? On Friday night when I shut down at the end of the day I got a message to say that Wndows was installing an update. I was asked not to turn off the computer or unplug the power and Windows will shut the computer down when its finished. OK sez I and went to bed. In the morning Windows was still doing its thing and telling me not to turn off the PC or unplug the power. Ten hours after shutting down I very warily turned the machine off and re-started. Nothing seemed to happen except that when I connected to the internet it began downloading furiously such that I could barely get any sites to load. Since then its been OK. I think I may have interrupted some update activity on Friday evening that then completed on Saturday morning. Maybe your problem was something similar seacue ?