Hi, found this on Microsoft web site:
Q. Are Office Word 2007 files backward compatible?
A. Office Word 2007 includes support for the new Microsoft Office Open XML Formats, compact, robust file formats designed to enable improved integration with external data sources and systems. The Office XML Formats are compatible with Microsoft Office 2003, Microsoft Office XP, and Microsoft Office 2000 with the addition of a file format converter patch, available from Microsoft Office Online and Microsoft Update. Users of Microsoft Office 2003, Office XP, and Office 2000 can open, edit, and save files using the new Office XML Formats.