Michael Linenberger, whose Total Workday Control is my most recommended guide to serious Outlook productivity, has just authored an excellent and comprehensive guide to making the transition from Outlook 2003 to Outlook 2007 using his methodology. In his typical fashion, the articles are extremely easy to follow and well-illustrated. If you have a copy of TWC, you'll be up and running in the new version of Outlook in a short while.
If you haven't yet read this book and count on Outlook to be the dashboard application for your day, there is no better guide to maximizing the application's potential in my opinion. Disclosure: I wrote the Foreword to Mike's book because I was so taken with the work he's done. Check out the book site for more information.
Mike is also the author of Seize the Workday – the best book on wringing maximum productivity out of a Tablet PC. Yes, I am a big fan.