Tech ARP published the planned RTM schedule of Windows XP SP3

Microsoft clarified that there will not be any integrated SP3 release for Windows XP Media Center Edition or Windows XP Tablet Edition. That means you won't be able to buy or obtain a complete Windows XP Media Center Edition / Tablet Edition SP3 CD. In addition, users of Windows XP Media Center Edition or Windows XP Tablet Edition will only be able to update to Service Pack 3 through Windows Update.

Windows XP SP3 RTM Confirmed