Shutting down Users PC’s – 2000 Domain

Any one know of a program that will shut down a windows 2000 Pro and possible a windows 98 machine at a given time. I know I can set up log off times for the domain to lot them off but I want there computers logging out and better yet, shutting down. I have users who keep every program you can think open and then leave for the day. These include outlook, word, excel, and our custom quoting and database programs. All need to do maintance at night. Any help will be greatly appreciated.