Okay. Lets do some simple math. Microsoft has spent 10000(Staff)*36($/Hour)*2000(hours/year)*5 (years) = 3.6 Billion Dollars. Lets bump it up to 5 billion dollars. Now the client division pulled in around 3.3 billion dollar profit in the last year 4th quarter http://www.microsoft.com/msft/earnings/FY08/earn_rel_q4_08.mspx. Lets assume 50% of it is due to Vista licensing. This means they need around 3 quarters to make up all the money they spent on Vista.
Now the home for you. Write down. Go and calculate how long vista has been in the market and how long ago they broke even on Vista.
Also remember among those 10K staff, i doubt there will be more than 5 K engineers and managers who are directly working on Vista. Many of them would be shared resources and adminstrative staff.
Surprise due today. Also the rent.