Microsoft has released a checked build of Windows XP Service Pack 3 for developers

This installation package is intended for IT professionals and developers downloading to a machine intending to debug or develop software on Windows XP Service Pack 3.

DO NOT CLICK DOWNLOAD IF YOU ARE AN MSDN SUBSCRIBER SEARCHING FOR FULL DEBUGGING SYMBOLS FOR WINDOWS XP: A more appropriate download is now available to MSDN subscribers on the Microsoft Developer Network.

Windows XP Service Pack 3, Checked Build