Exchange 2010 System Requirements

x64 based computer with Intel processor that supports Intel Extended Memory 64 Technology (Intel EM64T) or AMD processor that supports the AMD64 platform.

Intel Itanium family IA64 processors are not supported.

Microsoft Windows Server 2008 x64 Standard or Enterprise Edition with Service Pack 2 or Microsoft Windows Server 2008 R2 Standard or Enterprise Edition.

Minimum of 4 GB of RAM per server plus 5 MB of RAM recommended per mailbox.

Minimum of 1.2 GB on the drive used for installation.

500 MB additional disk space for each Unified Messaging language pack installed

200 MB of disk space on the system drive.

DVD-ROM drive for install media

source: http://www.microsoft.com/exchange/en-us/system-requirements.aspx