A new version of IE has been released, and with it more confusion about which is the right version of MSXML. Adam Wiener clarifies the situation.
Of the many versions of MSXML, only two versions are recommended for use in IE. Version 6, the newest, and version 3, the most widely available, will be receiving the bulk of support such as bug fixes.
Wiener recommends that version 5 should not be used at all. This was designed specifically for Office 2003 and later, and will trigger an ActiveX warning in IE 7.
Version 4 has been replaced by version 6 and "and is only intended to support legacy applications".
Older versions like 2.6 have been "kill-bitted" and are no longer available in IE.
Wiener offers on its history of MXSML and a script for selecting the correct version on his web log.