Comparison of Augustine and Plato

Augustine seems to have practically plagiarized Plato. Substitute "god" for "the good" and "the divine" for "the forms" and there you have it: Augustine's philosophy. He even adopts the technique of argument by analogy from Plato. It is interesting to note the inconsistencies in Augustine's own comparison to Platonic theory. Plato considered the forms to be the greater knowledge attainable only by philosophers and those with a truly rational soul. Thus, understanding of forms is a rational process which Plato attributes to the power of human intelligence, counterpoising it to the "inspiration" of poets. In fact, this is the basis for Plato's entire assertion that philosophers not only should be rulers, but are the only people fit to be rulers if the aim of a society is justice.
Augustine seems to accept this general theory of Plato's, but he then proceeds to extend it to the realm of Christianity. The various forms which Plato believes are the realm of the "intelligible" or the "rational" are the very definition of god for Augustine. In other words, Augustine accepts Plato's theories and then redefines the realm of knowledge and forms as god himself. It is an interesting technique, but not completely in keeping with Plato. Where does this sudden redefinition come from? Does it follow the ideas of man's intellectual capacity for reasoning stressed by Plato?
The concept of a tripartite agency of existence: body, soul, and god, does not completely parallel to Plato either. Plato believed in the physical world, the world of forms, and the greatest form of all: good. A superficial inspection would correlate these to body, soul, and god respectively, but this cannot work. First off, the world of forms, in Platonic terms, equates to god himself according to Augustine. The greatest form of all, however, can be no other than god as well. Plato's third realm, the realm of the perceivable, then must correlate to both Augustine's "body" and his "soul." This, however,