Here's what Anu's wordserver says about personification:

Personification \Per*son`i*fi*ca"tion\, n. [Cf. F. personnification.]

1. The act of personifying; impersonation; embodiment. --C. Knight.

2. (Rhet.) A figure of speech in which an inanimate object or abstract idea is represented as animated, or endowed with personality; prosopopeia; as, the floods clap their hands.

It stands to me that prosopopeia is just a fancy way of saying 'personification', except for expressing 'speaking as if being an imaginary person' which, I would say, definitely exceeds p..n's definition.

So, a man posting here and claiming to be Albert Gore would (probably, not necessarily) be guilty of a nasty personification, whereas the same man, introducing himself as the 43rd President of the US of A, could only be called a prosopopeia enthusiast!