Yes.
I did take biochem in undergrad (1 year not counting molecular bio and other stuff). It was my major. It did help me a lot in my med school biochem class. People who hadn't taken biochem before found the med school one challenging but survived.
Remember that there is a lot of variation in undergrad classes so you can't really compare things this way. I'm sure some undergrad biochem courses are similar to med school biochem or cover the same material (mine mostly did, but again over a full year and in more detail with different emphasis).
NO. This is like trying to prepare for a car crash by hitting your head against a wall. If you got in to med school, you can succeed at the curriculum. Wait til you get there and then do what they tell you. You do not have time or motivation before school starts to study anything in a way that will help you.
By the way this really isn't the right forum for this question.