We use a mix of VS2005 pro and VS2008 pro against a TFS2005 server. We do not have MSDN subs and we don't want to upgrade to VS2010 unless this financially reduces our costs of CALs. The licenses we have are from MSDN subs that we let expire when the recession started.
The retail version of TFS2010 may or may not come with 5 CALs (it's in a white paper somewhere, but the MS chap on the end of the phone had apparently never heard of this).
Additional CALs may cost several hundred pounds extra each (we think we need 3 more that the possible 5 included with TFS givint the required 8 in total). We can probably shop round for these for the best price.
Looking currently like a purchase of retail TFS2010 and three extra CALS is the best option, but it's taken several phone-calls and emails over several days to figure this out and even then we can't verify that this is correct.
We now need to balance these costs against the costs of MSDN subs (possibily as part of a VS2010 pro upgrade, possibly as part of standalone subs). After all of this we need to convince the company partners that this is a worthwhile purchase to reduce the large amounts of time we spend waiting for TFS2005 to branch and merge.