Two very interesting developments are happening that will improve Word 2007’s MathML support. The first is key for helping in getting Word 2007 math text into the scientific and technical publisher workflows and the second may help in this regard too. Specifically new transforms are now available in beta versions enabling Word to read and write MathML. These XSLT files are responsible for converting between Word’s native math format OMML and MathML 2.0. If you’d like to try out the new files (omml2mml.xsl and mml2omml.xsl), you can download them from the Microsoft Connect site using the invitation code: 0707-84P4-DPWT. Once you’ve downloaded the files, copy them to C:\Program Files\Microsoft Office\Office12 subdirectory, or wherever winword.exe is. Before doing so, you might want to change the current omml2mml.xsl and mml2omml.xsl files to omml2mml.xsl.bak and mml2omml.xsl.bak, respectively, in case you want to back out the update at a later date. But I doubt you will. The new ones are significantly better.
The second development is that Word 2007 will have a service pack release that enables it to read and write the ISO standard odf files as well as the native ISO standard OOXML files. In the odf standard, math zones are represented by MathML 2.0. So when Word converts to and from odf, it will use MathML 2.0 for all math zones. And it will use the files above to do the translations.