Microsoft has released Windows XP Service Pack 3 (SP3) to the public through Windows Update and Microsoft Download Center, after a slight delay. The SP3 was delayed due to a bug in Microsoft Dynamics Retail Management System (RMS).
Although downloads are available on Automatic Updates, people who want to download the standalone package can use following official links to download SP3
(Supported Operating Systems: Windows XP Home Edition; Windows XP Professional Edition; Windows XP Service Pack 1; Windows XP Service Pack 2)
>>Windows XP SP3 exe file (342.9Mb)
>>Windows XP SP3 ISO Image (544.9Mb)
>>Windows XP Service Pack 3 Network Installation Package(316.4Mb)