Austria is a hidden civ in CIV III. You must remove an existing civ (most preferably Byzantines) to play as Austria. It's leader is Charles V.
Civilization V: Gods and Kings
Austria will make its proper debut in the Gods and Kings expansion coming out in June 2012. Its leader will be Maria Theresa.
Capital: Vienna
UA: Diplomatic Marriage - Can spend money to annex or puppet an allied city-states into their empire without conquest.