This is shaping up to be a pretty cool month. Last week we finally had the first public draft of Ecma's Office Open XML format standard released. Now today the first public beta of Office 2007 has been released.
I'd really encourage everyone to head up there and download a copy. It will give you a great chance to start working with the file formats and building solutions. Between the openxmldeveloper.org community and the Ecma draft, there should be a ton of information available to help you get started. Also my blog will continue to focus on the file formats for a long time to come, so you can always check back here too.