SourceForge.net: ODF Add-in 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.

Still beta, but next year we should also see converters for excel and powerpoint!

BTW, the OpenOffice product looks surprisingly like MS - so far.