folder permissions

Have a network of 50 users, running win2000 and 98 workstations. Server is NT4 Server. Each user has a folder for work on the file server. On their folder they have modify permission. When they create a folder in it they have the ability to change permissions. We want them to only have modify so as not to lock out the administrator. How can this be done without having to go in and change ownership of files when they are created?