To stop Windows Messenger from signing you in automatically
If you do not want to be automatically signed in when Windows Messenger starts running, you can remove your .NET Passport as the default on that computer.
Go to User Accounts in the Windows XP Control Panel (Start, Control Panel).
On the Advanced tab, click Manage Passwords.
In Stored User Names and Passwords, select Passport.Net\*, and click Remove.
This does not delete your Passport, but removes its connection with your computer.
Click Close, and then click OK in the dialog box.
Note
If you click Sign me in automatically in the .NET Messenger Service sign-in dialog box, you will reestablish the Passport you use there as the default for that computer.