Although memorizing the login credentials is convenient, it creates a security risk. It is often required to purge all the stored credentials to make sure they are not used by unauthorized third parties.
Login credentials used by 802.1X authentication can be purged in exactly the same way they are cleared in Windows XP. There's more convenient means in Vista; especially in case of multiple users. All you should do is to uncheck a checkbox at the Network's Properties dialog window.
The steps are:
1) Right-click the Network and Sharing Center icon, navigate to Network and Sharing Center.
2) Click the Manage Wireless Networks link (see Tasks on the left).
3) Select a network, double click it, choose Security tab on its Properties window.
4) Uncheck "Cache User Information for Subsequent Connections" and click OK to save.
