Helping people with computers... one answer at a time.
Some methods for rebooting a computer remotely will cause a message to be displayed on that machine's console. That message can sometimes be disabled.
Is there a way to suppress the dialog box when remotely rebooting a Windows XP machine?
It depends on how you perform the reboot. If you use Remote Desktop to connect to the machine and shut it down via the menu or Task Manager's shutdown menu I believe there's no message box. The Windows Shutdown tool presents a message, if I'm not mistaken, when using it remotely. I believe that SysInternals psshutdown will allow you to control whether or not a dialog is shown.