If you follow Microsoft technology closely, there were a few webcasts from Bill Gates recently that provided a comprehensive overview all the platform. Here are the links:
First, there's the keynote at the CEO Summit:
Then, there was the keynote at the SharePoint Conference:
Last, there was be a keynote during the WinHEC (Hardware Engineering Conference), which included a lot of information about Virtualization and announced the Beta 2 for Windows Vista, Office 2007 and Windows Server "Longhorn":
Three keynotes in 8 days. Talk about a busy schedule...