The tool starts with the question if you want to evaluate your current setup or are planning for a new environment. After that you need to select the required architecture, Standard for small to medium sized organizations or Enterprise for large organizations (e.g. combined Exchange Server roles). You can define the required level of protection (i.e. number of engines on Edge, Hub Transport and Mailbox Server roles) and see the predicted effect on the hardware requirements. After completing the questionnaire you receive the recommended hardware configuration.
You can also see the predicted performance for different setups, i.e. virtual or non-virtual setup, Windows Server 2003 or Windows Server 2008 R2 as well as Exchange level (2007 or 2010).
You can download the FPE capacity planning tool here.