The Forefront Threat Management Gateway (TMG) 2010 Capacity Planning Tool helps customers understand what hardware they need in order to support the number of users, wide area network bandwidth, features and protections enabled in their Forefront TMG 2010 deployment.
Just download and open the Excel Spreadsheet to help figure out if what you have will work or what you’ll need.
http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=15196
