This book by Stan Reimer is an excellent guide to migrating your Exchange 5.5 organizations to Exchange 2000.

The book begins by explaining why you should consider upgrading to Exchange 2000 by comparing the new platform with earlier versions of Exchange. 

The author then goes on to the meat of the book--the North America Air business scenario. The treatment of this scenario is what sets this book apart from the pack. Most Exchange books include a number of short examples or scenarios to illustrate different aspects of the software, but these scenarios are usually simplistic and have little connection with the real world. The author however, who has considerable real-world experience in Exchange migrations, bases the entire book on a detailed analysis of a single large-scale Exchange migration for a fictional company called North America Air. This approach provides an excellent context for the technical content of the book and enhances its usefulness.  

As the author works through the scenario all the necessary steps of an Exchange migration become self-evident: planning, migrating to Active Director, using the Active Directory connector, migrating a site, ensuring coexistence with downlevel Exchange servers, and completing the migration. The author then goes on to cover managing, monitoring, and maintaining an Exchange 2000 organization.

I highly recommend this book and give it  stars out of five, and you can find it on Amazon here.