Server is Windows 2000. One of the names is EVERYONE. Is this the same as IUSR_machinename? because there is not one of these.
Everyone is a GROUP, not a user. The everyone group includes (go figure) every user.....including the GUEST account. So any permissions you assign to Everyone will be granted to every user, including the guest account.
check in the the proper domain to which ur computer belongs to and also click the "show all users" button