Microsoft confirmed officially that Windows XP Service Pack 3 will be made available for download in the next couple of weeks. It seems that Microsoft is continuing the practice of releasing the milestones of the first service pack for Windows Vista and the third refresh for Windows XP concomitantly. The Redmond company initially shipped a pre-beta build of Windows XP SP3 concomitantly with the pre-beta version of Windows Vista SP1 in mid July. Up until this point, Microsoft has been dead quiet about the development of XP SP1, with all details

stopped by the Windows Omerta codename Translucency, set in place by Sinofsky.
Now Microsoft has confirmed that the full beta of the service pack for Windows Vista will be available for download via Connect to some 10,000 to 15,000 testers. Additionally, the Redmond company also announced that the first actual beta of Windows XP SP3 will be delivered to all TechNet and Microsoft Developer Network subscribers. The third refresh for XP is planned for limited availability by mid September. At this point in time, Microsoft failed to reveal if a public beta of the service pack will be offered to users, in a manner similar to that of Windows Vista SP1.
However, unlike Vista SP1 which only now had its final availability date confirmed for the first quarter of 2008, Windows XP SP3 was scheduled all along for the first half of the coming year. In mid July, Microsoft delivered to a select pool of testers Windows XP SP3 pre-beta build 5.1.2600.3180 (xpsp.070718-2058). The version was subsequently leaked to peer-to-peer file sharing networks. Microsoft emphasized that the third service pack for Windows XP, as well as the first service pack for Windows Vista, would not impact considerably the users’ experience on each of the two operating systems. Still, XP SP3 is long overdue as Microsoft delayed the product from 2006, to 2007 and then to 2008. The last refresh, for Windows XP, SP2 was made available back in 2004.

source- softpedia