I have a notification that flashes up for a second when I boot up as well. It is the Windows Security Centre telling me that I have no anti-virus protecing my computer. It does this before my Norton AntiVirus has a chance to load, which it does a fraction of a second later and the notification banner vanishes then. I barely have time to register what it says.
This is a fairly new development that started after on of the recent downloaded Windows XP Updates from MicroSoft. It also insists on reminding me to turn on Automatic Update. Screw that! I'll update at MY convenience and discretion, not automatically.