Last week we posted the Windows XP SP2 Platform SDK RC1 image on the download center. You can use the image to get the header files you need to build projects specific to this service pack. Here's the link and a blurb:
Microsoft Windows XP Service Pack 2 Platform SDK RC1
The Platform SDK – Windows XP Service Pack 2 Release Candidate contains the information you need to develop applications for Microsoft Windows XP Service Pack 2 Release Candidate 1. Use this SDK to ensure that you have the latest documentation, samples, and SDK build environment (header files, libraries, and tools) for the RC1 release of Windows XP Service Pack 2.
We'll headline more XPSP2 stuff this week, so keep an eye out.