The actual title is "Changes to Functionality in Microsoft Windows XP Service Pack 2". You can read the entire article from this link.
There are any number of reasons you might have to/want to do this. TechRepublic's got this article on how to do it.
If you don't want to take the time to download it you can order XP Service Pack 2 on CD from Microsoft. Follow this link. It's free.
SP2 hits the support tools, too. These aren't isntalled by default, you have to explicitly install them from the SupportTools folder on the XP installation CD. Anyway, this KnowledgeBase article (MSKB 838079) describes the tools and the updates.
This site is probably the most useful reference I've seen that discusses what you can do with .htaccess.
If you've followed my other entries about Remote Desktop, you'll note that one of the ways to connect to a remote system requires you to connect to to the SSH client running on your local machine by specififying an IP of 127.0.0.2. SP2 shuts this down. Well, it looks like Microsoft has rethought this and has issued this hotfix (MSKB article 884020) to address it.
There's some other, somewhat related information in MSKB article 817293, too.
Microsoft has put up this KnowledgeBase article (842242) to help with some of the problems caused by SP2. It's title is "Some programs seem to stop working after you install Windows XP Service Pack 2".
RSSCalendar.com let's you put your calendar online, retrievable with RSS. Good concept. Looks like it's an early implementation, though, cause there's no way to import a calendar and, let's face it, who's wants to reenter all those dates? Free sign-up.