[mikester]

Just a few things;

Require Users to log in - no auto logon functions.

Require users to lock the console before they walk away and if they can't be responsible enough to do that set the screen saver with a 2 minute threashold of inactivity requiring a password to unlock.

If you want to go deeper - make sure the built in firewall is on and that no incoming connections are accepted (the default value).

SP2 is a good next step as it make administering the firewall easier.

IS it XP Home or pro?