Exchange Server 2007 SP3 provides further flexibility with the addition of Windows Server 2008 R2 support for server roles and Windows 7 support for the Exchange management tools. These additions, along with enhancements for the advanced protection options against e-mail security threats, such as spam and viruses and the tools which help manage internal compliance and high availability needs provide Exchange administrators with the tools they need to manage their Exchange 2007 environments efficiently.
Clean installations of Exchange 2007 SP3 on a new server are possible by using this download in the same manner as you would install Exchange 2007 RTM, Exchange 2007 SP1 or Exchange 2007 SP2.
Exchange 2007 SP3 supports the installation of the Exchange 2007 management tools on a computer that is running Windows 7. Additionally, Exchange 2007 SP3 provides support for the installation of the Exchange 2007 Management Tools together with the Exchange Server 2010 Management Tools on the same Windows 7-based computer
For an overview of the new features that are available in Exchange Server 2007 SP3, see "What's New in Exchange Server 2007 SP3".