I just want to start to make you aware of the fact the Windows XP SP1 will get out of support on October 10. From this point we will no ship any security updates anymore for this servicepack.
Our normal lifecycle policy says that we are supporting a Service Pack for one year after the release of the next one. With SP2 we have been supporting it for 2 years.
More information: http://support.microsoft.com/gp/lifean19