You can stop Windows XP from using the cached login credentials for 802.1X authentication, and delete the information. This is useful if there are multiple people using the same computer, and one is already authenticated and another wants to login with their own username and password. Unlike with Vista, you must modify the Windows Registry and delete the following key in XP:
Hive: HKEY_CURRENT_USER
Key: \Software\Microsoft\Eapol\UserEapInfo
