Edit C:\Windows\PolicyDefinitions\Setup.admx

??<?xml version="1.0" encoding="utf-8"?>

<policyDefinitions xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" revision="1.0" schemaVersion="1.0" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
  <policyNamespaces>
    <target prefix="setup" namespace="Microsoft.Policies.WindowsSetup" />
    <using prefix="windows" namespace="Microsoft.Policies.Windows" />
  </policyNamespaces>
  <resources minRequiredRevision="1.0" />
  <policies>
    <policy name="ServicePackSourcePath" class="Machine" displayName="$(string.ServicePackSourcePath)" explainText="$(string.ServicePackSourcePath_Help)" presentation="$(presentation.ServicePackSourcePath)" key="Software\Policies\Microsoft\Windows NT\Setup">
      <parentCategory ref="windows:System" />
      <supportedOn ref="windows:SUPPORTED_WindowsXP" />
      <elements>
        <text id="ServicePackSourcePathBox" valueName="ServicePackSourcePath" required="true" />
      </elements>
    </policy>
    <policy name="SetupSourcePath" class="Machine" displayName="$(string.SetupSourcePath)" explainText="$(string.SetupSourcePath_Help)" presentation="$(presentation.SetupSourcePath)" key="Software\Policies\Microsoft\Windows NT\Setup">
      <parentCategory ref="windows:System" />
      <supportedOn ref="windows:SUPPORTED_WindowsXP" />
      <elements>
        <text id="SetupSourcePathBox" valueName="SourcePath" required="true" />
      </elements>
    </policy>
  </policies>
</policyDefinitions>

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