gmail-office2007
Use Gmail as Office 2007 to HTML converter

You need no hacks to read those Word 2007 files (docx) files without Office 2007.

Just mail all the Office 2007 document(s) to your own Gmail account and click the View as HTML link near the email attachment to convert those files into text / HTML format that can be viewed in the web browser itself.

docx-to-html
Gmail retains Docx formatting in HTML

This easy conversion method retains the document formatting (no images though) and works with docx, pptx and xlsx Open XML formats as noted by Chitu.