What should I get/ do to become a mountain bike racer?

I am an average novice bike rider. I want to know what I need to do to start training and eventually compete in mountain bike races. What kind of training and diet regiment should I follow? What kind of bike and helmet should I get? How do I even get into a race? I am looking for anyone who has experience in the sport who might be able to help an upstart wannabe racer make his dreams come true.