Finally the TMG 2010 capacity planning tool is released. The tool will allow you to calculate the WAN bandwidth and number of users a particular a hardware configuration will support, and can recommend server hardware based on the features, bandwidth and users your deployment needs to support.

The tool can be downloaded from here http://www.microsoft.com/downloads/details.aspx?FamilyID=01b2f7a5-8165-4ead-9693-994504f66449&displaylang=en