If you would like to shutdown or reboot a remote Windows XP or Windows Vista computer that is located on your network and you have administrative access to it; you may use the command below via the CMD prompt or the RUN prompt from any other Windows XP or Windows Vista computer on your network:

To Reboot:
shutdown -f -r -t 0 -m \\computer

To Shut Down:
shutdown -f -s -t 0 -m \\computer

'computer' being the actual name of the computer that you would like to reboot.
You may also use the IP address in place of the computer name.

The shutdown executable is located in %SystemRoot%\System32\ 
(More commonly C:\Windows\System32\)

Below is a list of the switches you can use with the shutdown command.  You may get this list yourself by typing 'shutdown /?' from the CMD prompt.

Usage: shutdown [/i | /l | /s | /r | /g | /a | /p | /h | /e] [/f]
    [/m \\computer][/t xxx][/d [p|u:]xx:yy [/c "comment"]]

    No args    Display help. This is the same as typing /?.
    /?         Display help. This is the same as not typing any options.
    /i         Display the graphical user interface (GUI).
               This must be the first option.
    /l         Log off. This cannot be used with /m or /d options.
    /s         Shutdown the computer.
    /r         Shutdown and restart the computer.
    /g         Shutdown and restart the computer. After the system is
               rebooted, restart any registered applications.
    /a         Abort a system shutdown.
               This can only be used during the time-out period.
    /p         Turn off the local computer with no time-out or warning.
               Can be used with /d and /f options.
    /h         Hibernate the local computer.
               Can be used with the /f option.
    /e         Document the reason for an unexpected shutdown of a computer.
    /m \\computer Specify the target computer.
    /t xxx     Set the time-out period before shutdown to xxx seconds.
               The valid range is 0-600, with a default of 30.
               Using /t xxx implies the /f option.
    /c "comment" Comment on the reason for the restart or shutdown.
               Maximum of 512 characters allowed.
    /f         Force running applications to close without forewarning users.
               /f is automatically set when used in conjunction with /t xxx.
    /d [p|u:]xx:yy  Provide the reason for the restart or shutdown.
               p indicates that the restart or shutdown is planned.
               u indicates that the reason is user defined.
                 if neither p nor u is specified the restart or shutdown is unplanned.
               xx is the major reason number (positive integer less than 256).
               yy is the minor reason number (positive integer less than 65536).

To Reboot:
shutdown /f /r /t 0 /m \\computer

To Shut Down:
shutdown /f /s /t 0 /m \\computer

'computer' being the actual name of the computer that you would like to reboot.
You may also use the IP address in place of the computer name.

Rebooting a computer called 'CoffinCM1972' on the network via the CMD prompt:

Shutting down a computer called 'CoffinCM1972' on the network via the Run prompt:

cmc