1st thing: you've got to have the Task Scheduler service starting automatically.
2nd thing: Write a .CMD or .BAT file that executes the steps that you need to perform. Some thing require a user be logged in, like printing to a printer. There are workarounds for this, but their a little complex.
3rd thing: In the command prompt, type AT /? This will give you the syntax necessary to use the AT command. You tell the AT command the name of your .BAT/.CMD program to run & at what time to run it.
Tip: Look in the Windows NT Resource kit for a program called WINAT, which is a GUI program that allows you to generate AT file commands, and avoids the Coomand Line Interface complexities