Together, these security technologies will help make it more difficult to attack Windows XP, even if the latest patches or updates aren't applied. These security technologies together are particularly useful mitigation against worms and viruses. To developers these technologies will have impacts on the applications that they create and the tools they use. This page contains resources to assist developers in dealing with these impacts.   

Go here for more information: http://msdn.microsoft.com/security/productinfo/XPSP2/default.aspx