JSI Tip 6541. How do I enable AMD PowerNow! functionality for a new installation of Windows XP?

Microsoft Knowledge Base Article 815624 contains the following summary:

By default, Windows XP and Windows XP Service Pack 1 (SP1) do not enable AMD PowerNow! technology for AMD PowerNow!-capable AMD Athlon and AMD Duron processors. To enable AMD PowerNow!, you must install the latest processor driver from Windows Update.

Note The necessary driver support for PowerNow! technology is already configured on most systems sold by original equipment manufacturers (OEMs).