The following example demonstrates retrieving the source of the Windows setup files.

Example:
procedure TForm .Button Click(Sender: TObject);
var
  reg: TRegistry;
begin
  reg := TRegistry.Create;
  reg.RootKey := HKEY_LOCAL_MACHINE;
  reg.OpenKey('Software\Microsoft\Windows\CurrentVersion\SETUP',
              false);
  ShowMessage(reg.ReadString('SourcePath'));
  reg.CloseKey;
  reg.free;
end;