Woody is correct. Book I deals with the understanding of God. Who is he. What are his attributes. How does he relate to creation.
The proper understanding of God is fundamental to proper theology.
The issue that the natures of Man and God are mutually connected (I have yet to read the article you posted) is speaking to the knowledge of Man and the knowledge of God.
Calvin argues that the true knowledge of God will bring us to true knowlege of Man. When we understand really who God is, this will bring us full circle to the correct understanding of who Man is. (This is NOT to say that man is God -I can see some arminians attempting to twist these words to say that very thing)
Calvin also goes on to say that the true knowledge of Man will bring us to a correct knowlege of God. But, according to Calvin, Man, in his sinful and depraved nature (post fall), cannot correctly understand himself. Calvin's contention of a true knowlege of Man is in the context of a perfect sinless man (pre-fall) and his understanding of himself.
Calvin goes on to argue that becuase of the fall, it is not possible for man to look inward and gain a true insight into God. He sees God, as is evidenced by the fact that all men profess a belief in something (even if they profess a belief that there is nothing), but he cannot come to a proper understanding of the true knowledge of God. Thus the need for special revelation in order to bring us the proper understanding of the true knowledge of God.
I hope that helps. I ~am~ going by memory from my Calvin's Institutes class over 12 years ago.
Jean
This could help explain all the different religions in the world. God has made Man in such a way that Man has an innate sense that God exists. But due to our sin nature our picture of God becomes perverted and in our attempt to worship this twisted view of God we get all sorts of false religions from animism to voodooism and everything in between.