Office 2007 and 2010 use XML-based file formats and the newly shipped Open XML SDK 2.0 (see announcement) is the tool to use for pulling data out or injecting data into your Excel, Word or PowerPoint documents – without the use of the object model. This makes the SDK a primary tool for light-weight (i.e. no client automation required), high performance manipulation or creation of Office documents on either the client or server. For example, suppose you had a SharePoint list item event where the event receiver uses the Open XML SDK to open an invoice template and then cranks out an invoice for each of the customers in your database. Very powerful! Although the graphic depicts a server process, from a programming perspective, the Open XML SDK provides a consistent programming model for developers whether they’re building solutions on the client or the server.
I’ll refer you back to the announcement link above since it has the link to the Download, contains the Release Notes and provides links to a wide range of resources so you can get up an running with the Open XML SDK 2.0.