I've rolled my own solution to this b/c we have a server that is lots happier when it gets a regular reboot. You can use any NT based OS should work - I've used NT 4.0 and w2k server and workstations in the past. Use the at command to schedule a command line shutdown utility. I can't recommend one in particular, but usually just search for "NT shutdown command line" in a search engine and take whatever is listed as free, or if you have the resource kit, there's one included there I believe.