Windows XP Service Pack 3 (XP SP3) is available for download from Microsoft’s servers (although not from Windows Update or the Download Center due to a compatibility problem with Microsoft Dynamics Retail Management System). This service pack for all 32 bit versions of Windows XP includes all previously released updates and a small number of features backported from Windows Vista.
Download Windows XP Service Pack 3 (English ; size approximately 317MB )
For more details, see the Microsoft whitepaper “Overview of Windows XP Service Pack 3”. For other useful articles about Windows Service Pack 3, see Ars Technica , PCMag.com and Lifehacker.