You can download it now from the Microsoft Download Center. This version supports the RC1 release of Windows Vista.
Here's a list of some of the more significant enhancements courtesy of Jensen Harris:
Improved support for the minimized Ribbon
Visual redesign of the "Northwest" corner of the programs
Double-click the Office Button to close the window
Silver color scheme
Redesign of the PowerPoint Home tab
Improvements to default styles for all objects (pictures, tables, charts, SmartArt, headers, footers, etc.)
Quick Customize Menu
New product icons
Usability improvements to the Office menu
Send button in the form in Outlook
Over 1000 changes (most minor) to the content of the Ribbon
The technical refresh requires that the Beta 2 release already be installed. You can get Beta 2 here.