If you are new to development with the Open XML Formats, take a look at this Open XML Online Training series and learn more about the Open XML file formats architecture, the Open XML schemas, the .NET packaging API, and programmatic generation of rich data-driven Open XML documents.
All my respect goes to Doug Mahugh for the amazing job he has done with the Open XML training. Microsoft is really lucky to have someone like Doug on board. I told you I had a chance to attend this training a couple months ago in Redmond and it really helped me understand Open XML. After that, Doug has traveled all around the world delivering that training, and being Doug he organized a video shoot of the training in San Francisco. He is just amazing! Today, this content is just a click away on MSDN and you can see Doug in action no matter where you are.
You can find all the videos at the Open XML Developer Workshop page on MSDN here.
You can also find training ppts, hands-on labs, and code samples here.