"Martin Plechsmid" wrote in
:

Look, for instance, at "C:\Windows" and choose Properties -
Security - Advanced. There you'll see permissions for
Administrators, System, Owner, Users and PowerUsers, all
non-inherited. No privilege for Guests (nor Everyone), though
users in Guests group see the folder and file content without any
problem. That's what I'm talking about. So, where the privileges
for Guests come from?


Martin,

That makes your question much clearer.
The best answer I have found comes from the article:

"Managing Authorization and Access Control"
http://technet.microsoft.com/en-us/library/bb457115.aspx

It seems to indicate that with a couple of exceptions the "Groups" and
"Users" groups are essentially one-in-the-same:

quote
Guests

By default, members of the Guests group are denied access to the
application and system event logs. Otherwise, members of the Guests
group have the same access rights as members of the Users group. This
allows occasional or one-time users to log on to a workstation’s built-
in Guest account and be granted limited abilities. Members of the
Guests group can also shut down the system.

Note: The Guest account, which is a member of the Guests group by
default, is not an authenticated user. When logged on interactively,
the Guest account is a member of both the Guests group and the Users
group. However, when logged on over the network, the Guest account is
not a member of the Users group.

/quote

Hope this helps,
John