Exchange Server 2007 is a modular system with five server roles: Edge Transport, Hub Transport, Mailbox, Client Access, and Unified Messaging. All roles except Edge Transport can be installed on a single server, but Hub Transport and Mailbox are required. The document discusses preparing a Windows Server 2003 machine for Exchange 2007 by installing prerequisites like IIS 7 and .NET Framework 2.0. It also covers installing Exchange 2007 via Setup.exe, configuring roles like Client Access and Mailbox, enabling Outlook Anywhere, and using the Exchange Management Console and PowerShell to manage the new server.