Client PCs can be set to automatically lock-out after a set period of time using Windows 'Group Policies' on the domain controller.  When a machine connects to the server, or when a user logs in, the applicable policies will get applied to the client PC.  To setup an automated inactivity lockout using the screen saver time, then follow the following steps:

• Log onto the Windows domain controller as an 'administrator'
• Search for 'Group Policy Management'
• Within the Forect|Domains|domain name area right click and "Create a GPO in this domain.." etc.
• Now drill down through "User Configuration|Policies|Administrative Templates|Control Panel|Personalization"
• In here set the following options
  • Enable screen saver - enabled
  • Force specific screen saver - enabled and set to "scrnsave.scr"
  • Screen saver timeout - enabled and set to 600 for 10 minutes
  • Prevent chaning screen saver - enabled
• Once this has been applied then 'Group Policy' can be updated on a selected machine by executing the command "gpupdate"