Access control lists
To really lock NT down hard, set the root directory to full access for administrators and system, list access to users (not Everyone). Let that work all the way down the tree. Loosen things up as need be, but what has been done is ensure that any new directory that gets created will have those permissions.
Make sure the print spool directory has full access to creator\owner (see the NT Resource Kit, 3.51 Update 1 (also known as vol 5)).
Go through (using cacls, or use the search facility of either file manager or explorer) and set the permissions on all of the executables and DLLs to full access to admins (or if people normally work on that machine under admin status, remove write permission for admins), and list only (read-execute) permissions to users.
Note that it is now difficult for users to install any software. This could be good or bad, depending on what you want to do. Make a list of common DLLs that are updated often and give users delete permission.
Now apply the "smoke test" - log in as a user, and see what is broken. Some programs insist on being able to write to an .ini file in the system tree - if users can't write to (or create) these files, these programs will fail. Change the permissions as need be.
Be careful, it is possible where non-admins either can't successfully log in, or get a desktop that is completely blank.
If users are allowed to store files locally, make sure that they have full rights to their own directories. Note that under NT 4.0, a user's desktop profile, and numerous other things are stored under the system tree - look in %systemroot%\profiles, and make sure each user has full rights to their subdirectory - it should be admin, system, and user have full access.
It is a good idea to loosen up the temp directory - a good thing is to give users list access, but creator\owner full access. There may be other directories that need work, depending on what apps are installed, and whether they have any notion of multiple users - one example would be the cache directory for a web browser.
Since people have a lot of different needs, there is no single answer - it depends on the environment.
As to user rights, go through and make sure Guest is not only disabled, but that it has no rights to anything.
Internet FAQ top