Windows XP supports two main types of environment variables – user variables, and system variables. User variables are applicable to the currently logged on user only, while system variables apply to all users of an XP system. Windows XP allows users to create or change their own user variables, but only an administrator can change system variables. In most situations, user variables will apply once a user logs off and back on, while changes to system variables require the system to be rebooted.
The main tool used to configure environment variables on an XP system is the System applet in Control Panel. From the Advanced tab, click the Environment Variables button. This opens the Environment Variables window. From this interface, environment variables can be added, edited, and deleted as necessary.