Scheduled Maintenace for win2k servers

Does anyone know where I can find a list of scheduled maintenace to perform on a win2k server including the recommended intervals. I hear a lot of admins say they down there 2000 servers for maintenace, and I am just wondering what maintenace does it entail. I have 3 2000 servers that I have not taken down since I set them up 6 months ago. Is there maintenance I should be taking them down for?