Windows XP Automatic Re-boot

Clarifications

I couldn't find anyhting within XP that would do what you ask but I did find a site that offered a number of programs that may fit your needs: http://pcwin.com/popular/Windows_Xp_Auto_Shutdown-3.htm

One option is to use the built-in shutdown command and set a schedule to implement it.

Here is an example (in the Workaround section);

http://support.microsoft.com/kb/814761

There are several nice freeware apps out there for this sort of thing. Sysinternals had one as I recall.

If you'd rather just use the tools within the OS, use task scheduler to do this.

Click Start, and then click Control Panel.
Click Performance and Maintenance, and then click Scheduled Tasks (unless you're in classic mode - then just click on Scheduled Tasks).
Double-click Add Scheduled Task. The Scheduled Task Wizard starts.
Click Next.
Under Click the program you want Windows to run, click Browse.
In the Select Program to Schedule dialog box, locate the %SystemRoot%\System32 folder, locate and click the Shutdown.exe file, and then click Open.
Under Perform this task, specify a name for the task and how frequently you want this task to run, and then click Next.
Under Select the time and day you want this task to start, specify a start time and date for the task, and then click Next.
Type the user name and password to run this task under, and then click next.
Click to select the Open advanced properties for this task when I click
Finish check box, and then click Finish.
Click the Task tab.
In the Run box, specify any additional parameters that you want to use with Shutdown.exe (you can see these if you open a command line with start run and enter shutdown /? at the prompt).
Click OK.

Hope this helps! Good luck.