Nice comments Psac and Amoment! I would think the only think that we could really trust as from God would be specifically what Jesus states and that is even depending on what outside sources can prove to us regarding Jesus.
Probably the whole bible is simply written by man, however; did they capture what Jesus did state as from God? Also, if Jesus can in some ways be proven wouldn't that mean that the lineage leading up to his birth and the fulfilled prophecies regarding his birth and life would have to be inspired by God??? And if that is true, then maybe some parts are and some parts are not directly inspired from God as AGuest said?