With Windows XP there isn’t a native way to manage power settings via a group policy setting. With Vista and Longhorn server this is now managable. Here is a link to the Energy Star website for a downloadable tool with an .adm file and a client application.

 http://www.energystar.gov/index.cfm?c=power_mgt.pr_pm_ez_gpo

Microsoft Whitepaper to lock down a Terminal Server

How to lock down a Windows Server 2003 or Windows 2000 Terminal Server session