If you go to XP's Help and Support and then click on Security and Adminstration you will find out what you require.
But basically a new User Account is done from the Create a New Account in the User Accounts window. When the New Account Name appears enter a name for it (perhaps the name of the person) and then click Next.
A window then requests you to pick an account type; you should choose either Computer Administrator or Limited by clicking the required link. Have a look at both if you have any doubts, reading the list of actions that can be undertaken by the account type.
When you have completed this, click Create Account button and it should appear in the User Accounts window.