Here are two articles on the da Vinci plugin for Microsoft Word, which is promising full fidelity transformations from Microsoft legacy binary formats to ODF from within Office itself.
The articles are extensive, covering the history of the ODF/OOXML arguments, including Massachusett's open file format policy, as well as technical and procedural/workflow aspects and ramifications of the converters.
Most people believe that full fidelity file conversion is impossible, largely influenced by the poor fidelity generally experienced in converting documents from one vendor's binary file formats to another vendor's binary file formats. The major reason some people transfer such beliefs to the daVinci plugin is that they do not realize the plugin works natively inside Microsoft Word. The Word program itself performs the conversions using its internal processes for native support of a file format. The da Vinci plugin triggers the native Microsoft Word conversion process, intercepts the output at precisely the right moment, and maps it to ODF. When opening an ODF document, da Vinci simply reverses the process (although there is nothing simple about what da Vinci does or how da Vinci does this).
Think of it this way. The Microsoft Compatibility Pack is a EOOXML plugin for older versions of Microsoft Office. If these versions of Microsoft Office can use a plugin to perfect a conversion process between legacy binary formats and EOOXML, the same process can be used for ODF. In fact, it's actually easier to perfect a similar conversion process to and from ODF instead of EOOXML, particularly for Microsoft. Easier in that the ODF specification is lean and clean by comparison and very carefully structured. Even easier if you have the blueprints for those binary file formats.
Here are some technical details on how the da Vinci plugin works, including a simplistic overview that is really a simple and elegant solution that leverages Microsoft's own XML conversion. The article also outlines some of the other Office to ODF converter projects and the manner in which they address the problem, usually leveraging OpenOffice.org's conversion engine.
When a user loads a binary document (or creates a binary document in Microsoft Office applications), the apps themselves convert the binary documents to IMBR (the Microsoft Office apps in-memory-binary representation).
The user works the document in IMBR mode. This means all application features, business process adaptations, assistive technology add-ons, whatever, are available and cooking without disruption or change.
When an internal MS conversion process of IMBR is triggered, daVinci intercepts the results, and maps to ODF. The ODF version is saved to file.
An internal conversion process is triggered whenever functions like save, save as, open, or open most recent is called for.
Perhaps the most interesting aspect of the da Vinci plugin is that it provides the ability for users to select ODF as the default file format within Office, providing the native support for ODF that Stafford Masie was expecting, and neither Novell nor Microsoft delivered on the promise, but rather it was the OpenDocument foundation.