A highly touted feature of XP is the ability to have multiple users logged on to one machine and switch quickly between them. Like Windows 2000, this is certainly possible, but is it really a very worthwhile feature? The theory behind it is if you step away from the computer and somebody else wants to use it in your absence, they can sign in to their own settings without closing the programs you are running. The usefulness of Fast User Switching really depends on the type of work you do, how long each session lasts and how many users access each machine. Bear in mind that each additional user logged in is going to eat away at overall performance, especially if resource intensive programs are being run by multiple users.
To activate Fast User Switching:
Log in as Administrator[Start] [Control Panel] [User Accounts][Change the Way Users Log On and Off]Click [Use Fast User Switching]then click [Apply Options]Fast User Switching is now enabled.
To change users, click [Start] [Log Off] and [Switch User] when the [Log Off Windows] selection box appears.To log yourself off and leave the computer available for another user to log on, click the [Log Off] button. The Log On screen with the available users will be displayed.