Believe it or not, but Microsoft does not support Windows XP with XP SP3. Well, maybe that's not entire true. But it is true nonetheless. End users will find they they are unable to deploy XP SP3 on top of XP. What is the catch? You just have to think of XP not as a single version but as a continually evolving product. In this context, XP SP3 does not support Windows XP RTM. XP was released to manufacturing back in 2001, and the original version
of the operating system is no longer supported by Microsoft.

This is also valid for the currently available Standalone Update Package for Windows XP Service Pack 3 Release Candidate. Under System Requirements and Supported Operating Systems, Microsoft enumerates: "Windows XP; Windows XP Home Edition ; Windows XP Home Edition N; Windows XP Media Center Edition; Windows XP Professional Edition ; Windows XP Professional N; Windows XP Service Pack 1; Windows XP Service Pack 2; Windows XP Tablet PC Edition." But at the same time the company offers a little note pointing to XP SP1 or SP2.

Users will be able to integrate SP3 on top of Windows XP SP1 or Windows XP SP2 with absolutely no problems. However, they will not be able to do the same with XP RTM. This because support for XP RTM has been retired for quite a while. Windows XP Home Edition Service Pack 0 (RTM) and Windows XP Professional Service Pack 0 (RTM) are no longer supported since 30-August-2004. With support retired for Windows XP Media Center Edition 2002 Service Pack 0 (RTM) one year later, on 30-August-2005.

Otherwise you're good. You can easily jump from XP SP1 and XP SP2 to XP SP3. You might ask at this point who is still using the RTM version of XP or even XP SP1? Well, there are always exceptions that confirm the rule. And if XP SP2 is the rule then...

Source: http://news.softpedia.com/news/Microsoft-XP-SP3-Does-Not-Support-Windows-XP-76472.shtml

I also think that RTM will have no problem with the SP3. I will try to integrate it.