Neowin has published the release dates of the third service pack for Windows XP. The general public will be able to download the final version on April 29 and on June 10 Microsoft will roll out the automatic updates.
April 14, 2008: Support is available for the release version of Service Pack 3 for Windows XP
April 21, 2008: Original Equipment Manufacturers, Volume License, Connect, and MSDN and TechNet subscribers
April 29, 2008: Microsoft Update, Windows Update, Download Center