windows messenger signs in when I don't want it to

[monkeyinthebush@hotmail.com]

I have windows messenger and MSN messenger installed
because some of my friends have windows version and some
have MSN version, and apparently netmeeting is not
supported for MSN users when the other user is using
windows msgr.
My problem is, when I sign out of MSN messenger so I can
play a video game or whatever, windows messenger signs me
back in unbeknownst to me, then I get annoying pop-ups
right in the middle of my game.
How do I stop this auto sign in?
Thanks for any help,
Frank J