Kim Komando has nice little writeup of the Microsoft Shared Computer Toolkit for Windows XP in USA Today. Check it out:
Microsoft tool secures shared computers
... With the Shared Computer Toolkit, you can customize restrictions for different Windows accounts, which is especially handy if you have both young children and teens in the house. The toolkit also has additional safeguards to protect your computer. For instance, it prevents kids from making changes to your system settings.