an XP host can have only one session viewing the desktop--either local or
remote.  If the machine is not a domain member, Fast User Switching may be
enabled.  In this case, a user session remains in progress even if the
console is switched to another session, either via Remote Desktop, or via
switching at the physical console.  So--in this case, both users are "logged
in" but only one session can be interactive at a time.