Hi,
MSN Messenger 6.1 uses some of the components from Windows Messenger 4.6, so
you'll want to reinstall that.
Once you reinstall Windows Messenger you can 'disable' it so that it doesn't
keep starting up.
Go back to
http://messenger.microsoft.com and download Windows Messenger and
then install it.
Then follow the instructions below to disable Windows Messenger
To Prevent Windows Messenger from Running on a Windows XP-Based Computer
http://support.microsoft.com/default.aspx?scid=kb;en-us;302089&Product=WinMsgr
When you do this your Windows Messenger won't show up in your taskbar
anymore
However if you want to completely remove/uninstall Windows Messenger from
Windows XP can be found at this website made by Jonathan Kay.
http://messenger.jonathankay.com/problem.aspx?ID=7
Follow the steps and the pictures that the website has and you shouldn't
have anymore problems. Uninstalling Windows Messenger can disable some of
the messenger features such as Whiteboard Sharing, and others on MSN
Messenger if you're using that.