AirPort 4.2 for Windows
This update fixes compatibility with Wi-Fi Protected Access (WPA2) security software on AirPort Express and AirPort Extreme base stations. It also resolves issues with WPA2 on Windows XP with Service Pack 2 and Microsoft update KB893357.
For the latest information on AirPort software, check Software Update in System Preferences or the following Apple websites:
Internet service provider (ISP) compatibility:
Internet access requires a compatible ISP; fees may apply.
For more information on using AirPort Extreme or AirPort Express with your Internet account, contact your ISP or go to the AppleCare Knowledge Base at: http://www.apple.com/support