I recently had to look up some information regarding TFS Licensing (CAL’s and SQL Server), here is the white paper published by Microsoft on it: http://download.microsoft.com/download/7/B/1/7B18407A-AC79-4949-A318-A6636D96F497/Visual%20Studio%202010%20Licensing%20-%20Feb-2010.pdf
I wish it was a bit simpler, but at least the document covers all the bases.