Why does everyone think Obama is a freakin' Muslim?

I'm a freshman in High School, ranked number one in my cl, and am very interested in Politics. No one believes me when I say Obama isn't a radical Muslim terrorist incognito or the Anti-Christ like everyone at my school thinks.. My teachers aren't voting for him because they believe his faith isn't Christian. I don't agree with his plans and am all for McCain, but it drives me insane when people are ignorant about things and too stubborn to listen to anyone else. How did that get out that Obama is a "radical Muslim"?