MSXML 4.0 Service Pack 2 (SP2) is a complete replacement of MSXML 4.0 and MSXML 4.0 Service Pack 1 (SP1).
MSXML 4.0 SP2 provides a number of security and bug fixes. MSXML 4.0 SP2 does not replace MSXML 3.0.
MSXML 4.0 SP2 does not replace MSXML 3.0 because some obsolete and non-conformant features are no longer supported. You may run MSXML 4.0 and MSXML 3.0 and earlier versions concurrently.
MSXML4SP2 - an improved and easy to install version of MSXML 4.0.