Found this on the blog of Alain Leroy - Microsoft will bridge Open XML and ODF in 2007 Office System - check out the post, it has some interesting links as well. Also take a look directly at Sourceforge - ODF Addin for Word 2007
Open XML Translator provides tools to build a technical bridge between the Open XML Formats and Open Document Format(ODF). As the first component of this initiative, the ODF Add-in for Microsoft Word 2007 allows to Open & Save ODF documents in Word.Microsoft provides funding, architectural and technical guidance as well as project co-ordination. The project itself involves several partners - currently Clever Age, AztecSoft and DIaLOGIKa. If you take a look at the product roadmap you will see that a final release is scheduled for december 30th which will include both ODF to OpenXML and OpenXML to ODF translations.
PS This is actually a big thing in Belgium since Belgian government decided to standardize on ODF starting on September 2008 (Text in Dutch) , see also Alain’s earlier post – To ODF or not to ODF?