1. Install Word 2003 viewer (download from MS site)
2. Install Office 2007 compatibility kit (download from MS site)
3. Reboot (required for me so the docx extension was correctly registered
The next trick is that when I double click the document the converter from the compatibility kit kicks in but then the dumb thing launches WordPad instead of the 2003 viewer. So currently I’m forced to open the viewer first and browse to the docx.