Windows Messenger Automatically Sign Up

I am using Windows XP and using default Windows Messenger for contact/communication.
I am facing a problem; whenever I connect to internet my Windows Messenger automatically signs me, which I don?t want. For preventing sign up Windows Messenger I uncheck the option in the Outlook Express relating to messenger i.e. ?Automatically log on to Windows Messenger? but it still signs me whenever I connect to internet.
Pleas tell me how I can prevent the Windows Messenger from automatically sign up.