Windows Vista Annoyances

Start→ (Lock)

Also at the bottom of the Start menu’s right side, you’ll find this little padlock button. Clicking it locks your computer—in essence, it throws a sheet of inch-thick steel over everything you were doing, hiding your screen from view. This is an ideal way to protect your PC from nosy people who happen to wander by your desk while you’re away getting coffee or lunch.

All they’ll find on your monitor is the standard Logon screen described on Section 15.4. They (and even you) will have to enter your account password to get past it (Section 15.2.3).