Remove/Disable Cached 802.1X/PEAP Login Information (in Vista)
Like in Windows XP, you can delete the login credentials cached for 802.1X authentication in Vista. However, Vista offers an easier way. This is great if there are multiple users to one PC. You just have to deselect a checkbox on the Network’s Properties dialog box:
Right-click the Network and Sharing Center icon, and select Network and Sharing Center.
Click the Manage Wireless Networks link from the Tasks on the left.
Double-click the desired network and choose the Security tab on the Properties dialog.
Uncheck the Cache User Information for Subsequent Connections to this Network option, and click OK.