Actually, Administrator and Standard aren't the only kinds of accounts you can set up on your PC.

A third kind, called the Guest account, is ideal for situations where somebody is just visiting you for the day. Rather than create an entire account for this person, complete with password, hint, little picture, and so on, you can just switch on the Guest account.

The on/off switch is a tad buried; you have to open the Microsoft Management Consolea program intended for techies. The quickest way to get there is to open the Start menu and type comput. Double-click Computer Management in the search results and then authenticate yourself.

In the list at the left side, expand the Local Users and Groups flippy triangle; click the Users folder inside it. Double-click Guest; in the Properties dialog box, turn off "Account is disabled," and click OK.

Now, when the visitor tries to log in, she can choose Guest as the account. She can use the computer, but can't see anyone else's files or make any changes to your settings.

When the visitor to your office is finally out of your hair, healthy paranoia suggests that you turn off the Guest account once again. (To do so, follow precisely the same steps, except turn on "Account is disabled" in the final step.)