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.