When you leave your computer, you can prevent anyone else from using it by setting a password protected screensaver. Click on the Start button, point to 'Settings' and select 'Control Panel'. Double-click on the 'Display' icon and select the 'Screensaver' tab. Select the screensaver you want, set the wait time, and check the 'On Resume, Password Protect' checkbox. The password will be the same as your logon password.