http://support.microsoft.com/kb/314999

To logoff the user after a certain period of inactivity, you may use the Winexit screensaver which comes with Windows 2003 Resource Kit tools (free). Download Windows 2003 Resource Kit Tools from here

It contains the file Winexit.scr [Windows Exit Screen Saver].

Once installed, reboot the system.

Open C:\Program Files\Windows Resource Kits\Tools, Right-click winexit.scr and choose Install

The Display Properties dialog box appears with the Screen Saver tab active

The Logoff Screen Saver entry is automatically selected. Click Settings:S elect the Force application termination check box to force programs to quit. In the Countdown for n seconds box, type the value accordingly. In the Logoff Message box, type the message that appears during the logoff countdown. Click OK.  In the Display Properties dialog box, click Preview. You see the Auto Logoff dialog box. It displays the logoff message and the countdown timer. Click Cancel. Click OK. The Force application termination option forces programs to quit even if the programs contain unsaved data. If you do not use this option, programs that contain unsaved data do not quit and the user is not logged off.