Microsoft have put out a press release with some screen shots of the various apps in Office.

The look and feel is quite a departure from Office 2K3, etc and seems to be built around the Windows Vista (formerly Longhorn) interface with some stylistic "help" from SAP (the diagonal edges to tabs for instance).

Check it out at http://www.microsoft.com/presspass/features/2005/sep05/09-13OfficeUI.mspx