Straight from MSDN (EDIT: I'm assuming the "Technology Preview" would have the same requirements as MSXML4):
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Requirements
Platforms supported include Microsoft Windows® 2000, Windows NT® 4.0, Microsoft Windows Me, and Microsoft Windows 98.
For minimum functionality, the MSXML 4.0 Technology Preview requires the Microsoft Internet Explorer 4.01 Service Pack 1. For full functionality, MSXML 4.0 requires Internet Explorer 5.01 (or later). ServerXMLHTTP support is only available on computers that have Windows 2000 installed or on computers that have Windows NT 4.0 with Internet Explorer 5.01 (or later) installed.
In addition, support for the MIME Viewer and XMLHTTP is only available with Internet Explorer 5.0 (or later).
The MSXML 4.0 Technology Preview requires the Windows Installer. If you are running Windows NT 4.0, Windows 98, or Windows 95, you must first update your Windows Installer to version 1.1 before downloading the MSXML 4.0 Technology Preview. If you are running Windows 2000, you already have this installer and there is no need to reinstall this tool.
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Linkage for more info
HERE
Hope this is the info you were lookin' for.