Windows Vista made numerous changes with how user profiles work. In fact, the changes are too numerous to describe here (you can read more about the changes with user profiles in the Managing Roaming User Data Deployment Guide (http://go.microsoft.com/fwlink/?LinkId=73435). However, the policy settings for user profiles from earlier versions of Windows remain and Windows Vista introduces five new policy settings.
Four of the five new policy settings for user profiles exist under Computer Configuration\Administrative Templates\System\User Profiles (the remaining policy setting uses the same path under User Configuration). These five policy settings apply only to computers running Windows Server 2008 or Windows Vista, however; these policy settings can co-exist in GPO's applicable to clients earlier than Windows Vista. Operating systems other than Windows Vista ignore the policy settings. Let me begin with the policy settings under the computer configuration and then close with the single user setting.
The first of these policy settings is Delete user profiles older that a specified number of days on system restart. This policy setting accepts a numeric value, represented in number of days. Windows uses this value to determine the how long it retains dormant user profiles. When you enable this policy, Windows deletes all user profiles older than the value provided. This policy setting measures one day as 24 hours since the last time Windows loaded the profile.
NOTE: Microsoft released a hotfix to correct problems specific to this policy setting. You can view more about the issue and related fix from Microsoft Knowledgebase article 945122 (http://support.microsoft.com/?kbid=945122).