Microsoft Knowledge Base Article 306661 contains the following summary:
This article describes how to fax a document from a Windows program by using the Fax service in Windows XP.
To send a fax in Windows XP, you must first enable and configure the Fax service.
For additional information about enabling the Fax service, click the following article number to view the article in the Microsoft Knowledge Base:
306550 How to enable and configure the Fax service in Windows XP
For additional information about using Fax in Windows, click the following article numbers to view the articles in the Microsoft Knowledge Base:
306657 How to send a fax in Windows XP
306662 How to receive a fax in Windows XP
306663 How to fax a scanned document or image in Windows XP