XP Pro Service Packs can theoretically be applied to an XP Embedded image if the latter one has all the update required components
(starting from Windows Installer Service and others). However, it may not be an efficient way of upgrading XPe to SP2. You better
off creating SP2 based XPe image for the device. (even better add FP2007)
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Regards,
KM
PS. Just to be clear, XP Embedded is NOT a copy of Windows XP Pro.