Islam requires to believe in Allah and Mohammed as his prophet. Believing in Islam, believing in Allah, believing in Mohammed are all same thing: You can not ignore one of these concepts (alongside some others) and believing the rest; they coexist in theory.
And in every point of view, Mohammed stands in the middle of what you call Islam. He brought the subject religion, he brought the verses, he is the "ubermensch", it's his doctrine. There is no Islam without Mohammed; whether you are an unbeliever or a believer this is the fact for Islam, this is the core understanding and expectation of this religion.
Really?
I thought according to Islam, the Qu'ran existed before time. Doesn't that mean you could have it before Mohammed was even born? And what about those people between Adam and Mohammed, did God hate them?