http://www.servicefirst.com/KB/a156/how-do-i-schedule-my-server-to-automatically-reboot.aspx
Windows Server 2003
Navigate to Start -> All Programs -> Accessories -> System Tools -> Scheduled Tasks.
Click on "Add Scheduled Task".
You should now see the Add Scheduled Task Wizard. Click Next.
Disregard the list of programs, and click the Browse button.
By default, the browse button will bring you to the root of the C: drive. Navigate to WINDOWS -> system32 and locate the file named ‘shutdown.exe’. Highlight it, and click Open.
Enter your desired name for this task (such as "Auto Reboot"). Next, choose how often you would like your server to reboot, whether it is daily, weekly, or monthly.
Next you can select the time and date of the month you would like the server to automatically reboot. Click Next
Type in the password for the user you would like this task to run under. If you are setting this task to run under your ‘ServerAdmin’ login, enter the ‘ServerAdmin’ password. Once entered, click Next.
Place a check-mark in the option for 'Open advanced properties for this task when I click Finish'. Click Finish.
Add the following line in the Run field:
C:\windows\system32\shutdown.exe -r -t 00
You will need to enter your ‘ServerAdmin’ password to confirm the changes. Once entered, click OK.
You have now set Windows to automatically reboot as the time you have specified.
Windows 2008
Navigate to Start > Administrative Tools > Task Scheduler
Name the task to reflect the nature of the request. Click Next
The next two screens will allow you to set the frequency of the task. Do so then click Next as you are ready
Select "Start a program", then click Next
In the "Program/Script" box enter in "C:\Windows\system32\shutdown.exe." If this is a x64 bit operating system, you will want to use "C:\Windows\SysWOW64\shutdown.exe". Click Next when finished
The last screen will allow you to view the settings before creating the task. When ready, click Finish.
