Stephen Peront of Xinnovation has contributed this C#/.NET project that shows how to work with embedded objects in Open XML documents.  Here's his summary of the project:

"It is often necessary to embed Excel charts and sheets in Word or PowerPoint documents that must be updated or refreshed with real-time data and formatting. The ability to automate these updates using previous versions of Office required that the Word, PowerPoint and Excel applications be launched and visible. The quantity of code required, installation and configuration of required API’s and a lack of support for Office applications running on an application server made it near impossible to deliver enterprise ready software using Office in this scenario.

The new Open XML file formats used in Office 2007 make it easy to update Excel objects embedded in Word or PowerPoint without ever having to launch any Office application visually. Using Open XML you can develop more powerful document solutions that store and access information from Excel Server, SharePoint and various other content islands to put the innovation of business back into the hands of the workers."