Recently after installing Windows 7 and configuring Windows Backup to run weekly I found that if system was not running due to a Power Management sleep that Windows does not automatically wake-up to run the scheduled backup. This meant when I would login the morning after the backup was scheduled to run that Windows would kick into action and start the backup. Although I couldn't find instructions for this on the tubes, it turns out to actually be quite easy to configure Windows 7 to wake-up automatically for a scheduled backup.

First you need to configure WindowsBackup to run on a schedule by following this Microsoft guide:
Back up your files

After you've configured your backup schedule, open the Task Scheduler by clicking:
    Start > All Programs > Accessories > System Tools > Task Scheduler

Within Task Scheduler, click to:
    Task Scheduler > Task Scheduler Library > Microsoft > Windows > WindowsBackup

In the top-center window pane you should see a task titled AutomaticBackup that corresponds to the backup schedule item you created. Right-click AutomaticBackup and select the Properties menu item.

In the Properties Window, click the Conditions tab and then check the box titled Wake the computer to run this task.

Click OK and it's a done deal.