Selective use of MSN Messenger in multiuser XP

[mickey]

In a new XP Pro install, my wife clicked on a MSN Explorer
icon, where she is Admin and besides installing the entire
IExplorer file on the desktop OF ALL USERS - it also set
an MSN Messenger icon in everyone's tray.

One, why is it necessary to have TWO installations of
IExporer, and second how can we fix this computer so that
those who use MSN messenger have it in their trays, but
those - like me - who never use IMs escape the open ports
and shenanigans that follow ie clean it out?

Thanks in anticipation.