Apple Remote Desktop not running scheduled tasks - server is in Sleep mode

I'm a parent volunteer helping to administer a computer lab at my son's elementary school. the lab has 33 imacs (mix of G5 and early Intel imacs) and OS X 1.5 server running on a headless mac mini. We recently setup a second headless mini as an ARD server.
I created some scheduled tasks to execute daily log-off's and shutdowns, however the tasks did not run as scheduled. My question is, do I have to define the Energy Saver preferences on the ARD server to never sleep? Will ARD tasks still run if the server is in sleep mode?

One final question, if the client imacs are in sleep mode, do I need to execute a task to wake them prior to running the task to log-off/shutdown?

Thanks in advance for your advice and assistance.