Just in case that you were holding your breath while waiting for Service Pack 3 for Windows XP on 64-bit architectures, you can now exhale. No, the service pack is not here. And the fact of the matter is that it's going to be quite a wait until Microsoft will deliver an equivalent to SP3 for x64 XP.
The Redmond company is currently cooking the third and final service pack for Windows XP, but just the 32-bit version of the operating system, the one made available all the way back in 2001. Users should not expect the Redmond company to release SP3 for Windows XP Professional x64 Edition by mid 2008, because that will definitely not be the case.
Microsoft gave official confirmation of this in the Overview of Windows XP Service Pack 3 whitepaper: "Windows XP SP3 is for x86 editions of Windows XP only." Now, the truth is that 32-bit XP and 64-bit XP are separate products made available four years apart, as Microsoft released Windows Server 2003 x64 Editions and Windows XP Professional x64 Edition in April 2005, after Windows Server 2003 Service Pack 1 (March 2005) and Windows XP Service Pack 2 (August 2004).