What I could find on Vancouver Olympics:
http://www.olympic.org/Documents/Gam...y_2011_eng.pdf
Vancouver 2010 reached a record potential audience of 3.8 billion people worldwide and approximately 1.8 billion viewers.
That would be over the course of the whole event.
Montreal had the highest Summer Olympic US TV ratings up to 2008 (eventually beat by London):
http://tvbythenumbers.zap2it.com/wp-...summer2008.jpg