Microsoft KnowledgeBase article on WPA (Wi-Fi Protected Access) patch: Unlike some of the coverage of the WPA update to Windows XP, Microsoft's KnowledgeBase article is a model of clarity and straightforwardness. The update works only with network adapters that support Wireless Zero Configuration (the built-in XP wireless client support) in Windows XP. Windows 2000, 2003, and other drivers need to get updates from their makers.
The software enables WPA, but the article wisely points out, as some articles didn't, that each access point and adapter manufacturer must enable WPA in the individual pieces of hardware through firmware updates.
WPA replaces the broken WEP system with the interim 802.11i work, including a robust new key (TKIP), appropriate packet integrity (Michael or MIC, in which the checksum is an integrity check and in the encrypted payload), and adds 802.1x support for network authentication, as well as the consumer pre-shared secret option.