If the columns of each table have no distinct meaning unto themselves, then you want to use the join element:
http://www.hibernate.org/hib_docs/v3/re ... ation-join
If the tables do have meaning by themselves, then you want to setup some simple one-to-one mappings between 3 classes - ClassA and ClassB each represent table A and B, and ClassC has a one-to-one relationship with ClassA and a one-to-one with ClassB. (Like a Person has a Address and has a Car):
http://www.hibernate.org/hib_docs/v3/re ... n-onetoone