“Microsoft Windows XP Service Pack 3 is a rollup that includes all previously released updates for Windows XP, including security updates, out-of-band releases, and hotfixes. It contains a small number of new updates, but should not significantly change the Windows XP experience.”

http://technet.microsoft.com/en-us/windowsxp/0a5b9b10-17e3-40d9-8d3c-0077c953a761.aspx
Thanks Robert.