Microsoft has published a white paper on Windows XP Service Pack 3
>> Windows XP Service Pack 3 Overview
Windows XP Service Pack 3 (SP3) includes all previously released updates for the operating system. This update also includes a small number of new functionalities, which do not significantly change customers’ experience with the operating system. This white paper summarizes what is new in Windows XP SP3.
>> Windows XP Service Pack 3 Overview