How can i stop my windows messenger from autostarting ??

for yahoo messanger-login, go in preference and uncheck the box 'automatically starts yahoo messanger' for windows messanger-tools-options-preferences-uncheck 'run messenger when windows starts'

yes it depends the version of your messenger ,if is the version of default xp you need to disactivate from the registry

Are you talking about Windows Live Messenger? (aka, MSn messenger) In the Tools menu at the top, choos "Options." One the window for "General" options, uncheck the two options that make it automicaticall sign in when turning on the computer, or when logging on to the internet. That should fix it.