Processor: Intel Pentium or compatible 800-megahertz (MHz) or faster 32-bit processor or x64 architecture-based processor that supports Intel Extended Memory 64 Technology (Intel EM64T) or x64 architecture-based computer with AMD 64-bit processor that supports AMD64 platform
Memory: Minimum: 2 GB of RAM; Recommended: 2 GB of RAM per server plus 5 megabytes (MB) of RAM per mailbox
Hard disk: At least 1.2 GB of available disk space on the drive on which you install Exchange. An additional 500 MB of available disk space is needed for each Unified Messaging (UM) language pack that you plan to install and 200 MB of available disk space on the system drive.
Operating System: Exchange 2007 is specifically designed to run on computers that are running Microsoft Windows Server 2003. The domain controller that is the schema master must have Microsoft Windows Server 2003 Service Pack 1 (SP1) installed.