Windows 32bit Family XP RTM - 5.1.2600
XP SP1a - 1106
XP SP2 - 2180
Server 2003 RTM - 5.2.3790
Server 2003 SP1 - 1830
Server 2003 SP2 - 3959
Vista RTM - 6000.16386
Server 2008 Beta 3 - 6001.16510
Windows 64bit Family XP 64bit RTM - 5.2.3790.1830
XP 64bit SP2 - 3959
Server 2003 64bit RTM - 5.2.3790.1830
Server 2003 64bit SP2 - 3959
Vista 64bit RTM - 6000.16386
Server 2008 64bit Beta 3 - 6001.16510
Update: The build number for the final version of SP3 is 5512.
Update 2: It appears that Nick MacKechnie's blog post was removed later during the day. Nevertheless, the release schedule from his blog post can be found below.
Nick MacKechnie: 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.