MSXML 4.0 SP1 offers a number of new features and
improvements over the MSXML 3.0, including support for the XML Schema language
and substantially faster parser and XSLT engine. MSXML 4.0 SP1 is a complete
replacement for MSXML 4.0 RTM and provides a number of bug fixes. It can not
replace MSXML 3.0, because some obsolete and non-conformant features are no
longer supported. MSXML 4.0 installs side by side with MSXML 3.0 and earlier,
without any interference.