Start > run > type in: control userpasswords2 <enter> go to advanced tab > click passwordmanagement button > select the passport you don't want in the MSN inlog list (in this case your own) and click delete..restart MSN messenger, you'll see it's gone
Edit: after you've done that you have to type in your password everytime you log in..aslong as you don't tell MSN to save it, it'll stay like that.