This is just my speculation -- I have no info from Microsoft on this scenario -- but I'm expecting Windows 7 and Office 14 will be the main themes at PDC 2008.
When is Microsoft finally going to start sharing information on Windows 7?
After all, if the Redmondians stick to their own oft-quoted ship target of 2010 for the operating system, that is just two years away. For developers two years isn’t a whole lot of time when trying to make decisions about whether or not to build a new product that will be designed specifically to take advantage of new features and functionality in a new Windows release. And for IT managers struggling with deployment plans (as in deploy Vista now or wait two more years for Windows 7), that window on the next version of Windows isn’t overly wide, either.