From a newsgroup post: "Windows XP is just getting root certificate information from Verisign et. al. No evil plot here. If you want to turn this valuable feature off then go to Control Panel, Add or Remove Programs, Add/Remove Windows components, scroll to the bottom and uncheck Update Roo certificates. Downside is that you will no longer get the most up to date security information for what websites are secure and which are not".
Newsgroup post: "The updates will be downloaded, and not installed with your current settings. You will receive a notification in your system tray when updates are available. Just click the icon and you'll be given the opportunity to install them. Most of them, at this point are just test packages to test the feature, servers and etc. It will primarily be used to notify you of Critical Updates without having to go to the Windows Update site for them".