What is the difference between 'two way transactional replication' and 'peer to peer replication'?
generally transactional has a publisher and a subscriber, with some updating from the subscriber, peer to peer replication shares the same data in more of a node environment (often over long distances) and would be more suitable for load balancing.               

I'd go straight to technet for the overview    http://technet.microsoft.com/en-us/library/ms151196.aspx