To disable MSN messenger or Yahoo Messenger service during start up
1) Click on 'Start' ---> 'Run'
2) Type 'msconfig'
3) In the System Configuration Utility select 'Selective Startup'
4) Now click on the startup tab and deselect the messenger from the list of items. Usually it is 'MsnMsgr'/ 'MSMGS' for MSN Messenger/ 'YPager' for Yahoo Messenger
5) Click on Apply and then restart your computer.