is it possible to do an unattended install of service pack 2 on a user's computer without physically being there to run the setup or go to the Windows Update in the Start Menu??

I work as a helpdesk support person and I have a long list of computers that need the service pack 2 updates and I was wondering if I could do an unattended install of service pack 2 without physically being at each and every user's computer on the list.

Or does the unattended install only work when installing a fresh copy of Windows XP or XP slipstreamed with service pack 2??