Microsoft Knowledge Base Article 306214 contains the following summary:
This article describes how to create and use a password
reset disk for a computer that is a member of a domain. You can use a password
reset disk to gain access to your Microsoft Windows XP Professional-based
computer if you forget your password.
For additional information about how to create a password reset disk for a computer in a workgroup, or a computer that is not networked, click the following article number to view the article in the Microsoft Knowledge Base:
305478 How To Create and use a password reset disk for a computer that is not a domain member in Windows XP