The build number for the final version of SP3 is 5512. Windows XP SP3 has been released to manufacturing as of April 21st (US Time) with the release to web planned for April 29th (US Time). The detailed schedule by channel is below.
Windows XP SP3 - detailed by channel schedule
Channel / Release Vector
Planned dates (US)
RTM (release to manufacturing)
Windows XP SP3 Fulfillment Media
VL Customers via download
Microsoft, Windows XP, SP3, XP SP3, Build 5512, Release, Schedule