The easiest way to view the current values of all environment variables configured on your XP system is to issue the set command at the command line, as shown at left. To change environment variables (or define your own), use the Environment Variables window accessible from the System applet. Remember that you will need administrator-level access to change System variables, but that any user can change their variables in the User section. For a list of the various default variables available on Windows XP systems, see http://kennethhunt.com/archives/000933.html
Variables can also be changed directly within the Registry. For System variables, see HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment. For User variables, changes can be made in HKEY_CURRENT_USER\Environment.