Microsoft is announcing a licensing program for the new 2007 Microsoft Office User Interface. That means that individuals or companies will have opportunities to use Ribbon and other User Interface being used in Microsoft Office 2007 in their product and it's royalty-free, except if you are building a program which directly competes with Word, Excel, PowerPoint, Outlook, or Access (the Microsoft applications with the new UI), you can't obtain the royalty-free license (That means application such as OpenOffice.org will not be able to use this UI, but i think OOo team will come up with new idea of UI in the next major version).
Microsoft has provided a 120+ page document containing the guidelines that you will need to implement the Office-style UI. It's just a guide that should (but not always) help you when you had problems while implementing this new UI.
Although this new UI has brought a major changes, not everybody likes it, so please make a wise decision when you want to implement this new UI on your application, since not all of the users will like the new UI behaviour.
Jensen Harris' Blog
Microsoft Press Release
Office UI Licensing Site