Give these a try. They're from the (big) Platform Builder registry:
; @CESYSGEN IF MSXML3_XMLSAX
;
; MXXML Writer
;
[HKEY_CLASSES_ROOT\Msxml2.MXXMLWriter]
@="MXXMLWriter"
[HKEY_CLASSES_ROOT\Msxml2.MXXMLWriter\CLSID]
@="{fc220ad8-a72a-4ee8-926e-0b7ad152a020}"
[HKEY_CLASSES_ROOT\CLSID\{fc220ad8-a72a-4ee8-926e-0b7ad152a020}]
@="MXXMLWriter"
[HKEY_CLASSES_ROOT\CLSID\{fc220ad8-a72a-4ee8-926e-0b7ad152a020}\InProcServer32]
@="msxml3.dll"
"ThreadingModel"="Both"
[HKEY_CLASSES_ROOT\CLSID\{fc220ad8-a72a-4ee8-926e-0b7ad152a020}\ProgID]
@="Msxml2.MXXMLWriter"
[HKEY_CLASSES_ROOT\CLSID\{fc220ad8-a72a-4ee8-926e-0b7ad152a020}\Version]
@="3.0"
;
; SAXAttributes
;
[HKEY_CLASSES_ROOT\Msxml2.SAXAttributes]
@="SAXAttributes"
[HKEY_CLASSES_ROOT\Msxml2.SAXAttributes\CLSID]
@="{4dd441ad-526d-4a77-9f1b-9841ed802fb0}"
[HKEY_CLASSES_ROOT\CLSID\{4dd441ad-526d-4a77-9f1b-9841ed802fb0}]
@="SAXAttributes"
[HKEY_CLASSES_ROOT\CLSID\{4dd441ad-526d-4a77-9f1b-9841ed802fb0}\InProcServer32]
@="msxml3.dll"
"ThreadingModel"="Both"
[HKEY_CLASSES_ROOT\CLSID\{4dd441ad-526d-4a77-9f1b-9841ed802fb0}\ProgID]
@="Msxml2.SAXAttributes"
[HKEY_CLASSES_ROOT\CLSID\{4dd441ad-526d-4a77-9f1b-9841ed802fb0}\Version]
@="3.0"
; @CESYSGEN ENDIF MSXML3_XMLSAX