Transitioning from Exchange 2000/2003 to Exchange Server 2007
How a transition from Exchange Server 2000/2003 to Exchange Server 2007 is performed.
http://www.msexchange.org/tutorials/Transitioning-Exchange-2000-2003-Exchange-Server-2007-Part1.html
http://www.msexchange.org/tutorials/Transitioning-Exchange-2000-2003-Exchange-Server-2007-Part2.html
http://www.msexchange.org/tutorials/Transitioning-Exchange-2000-2003-Exchange-Server-2007-Part3.html