Windows XP/5.1.2600.1050.xpsp1.020529-1810

Only the express installer of this were available, which won't install the build due to needed files on MS servers no longer existing. The full setup executable was leaked on April 13th, 2015 by OSBetaArchive (OSBA) community.

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Reference: http://www.osbetaarchive.net/index.php?/topic/108-osba-release-a-week-ish-win2000-sp3-21954448-winxp-sp1-26001050/