when you say MSN, do you mean msn messenger? IF so
go to Start>Run and type msconfig
On the screen that appears there is a tab called Startup, here is a list of all applications that start when the machine starts. Untick msnmgr and click ok.
I advise you dont make any other changes unless you know what youre doing.
Tools, Options, General, and unclick the box that says "Automatically run Messenger when I log on to Windows"
Then when you start up your PC, MSN won't start up as well. You will need to click on the icon on your desktop to start it. On the sign-in page there will be an box you can click to reset it back to sign you in automatically if you want.