Consider the followings, but there r several more ideas u can get to search on the net.
1. Network and Directory Servers: In each Active Directory site where plan to install Exchange 2010, have at least one writable domain controller running. Take care for IPV6.
2. OS is recommended as 64-bit edition of Windows Server 2008 Standard with Service Pack 2
3. Hardware: x64 architecture-based computer with Intel processor, AMD processor that supports the AMD64 platform, page file size minimum and maximum must be set to physical RAM plus 10 MB, NTFS with 800×600 or higher. Memory as per applications install
4. It supports Outlook 2010, Outlook 2007 & Outlook 2003
5. Identifying Third-Party Product Functionality: Consider antivirus, backup, phone integration and fax softwares.
Here is more info: http://moss-exchange.blogspot.com/2009/11/exchange-2010-planning-and-coexistence.html