I have had two customers with the same story: their purchasing manager bought the entire development team Visual Studio 2005 Professional and now they want to start using Team Foundation Server.
What do they need to do in terms of technology and licensing to start using Team Foundation Server?
The technology component is easy: Install Team Explorer and off you go!
Licensing is pretty straight forward too - You simply need buy a Team Foundation Client CAL for the wanting to connect to the Team Foundation Server.
However in both of the cases i was dealing with with the development team found out these CALs are included role based products and now their question became:
"How do we upgrade from Visual Studio 2005 Professional to one of the Visual Studio 2005 Team System Editions(Roles)"
Unfortunately the simple answer is "You can not" - at least not easily.
What one of my customers did was return the Visual Studio 2005 Professional then as a new purchase buy the Visual Studio 2005 Team System Editions. Note if you go down this path apparently there is a 30 day+ restocking fee (we were able to get this waved).
-The other customer ended up staying with the Professional Editions.