AM2 CPU will not fit into an AM3 socket since it is a smaller socket. The AM3 CPU will fit into an AM2+ socket since it is smaller and was designed to be backwards compatable. They are two different sockets.
Yep they are two different sockets but AMD made their new CPUs so that they can fit and work in both AM2 and AM3 sockets... the only difference is one pin preventing the AM2 CPU from fitting in an AM3 socket. Even is somehow you fit the AM2 CPU in the AM3 socket, the AM2 CPU does not have the necessary controller for DDR3 ram.