i don't see the relevancy of how 6-year program students have to do with your biochem insecurities.
chances are that the people who are going to know more biochem will be the other traditional students that will be joining you (and have had previous biochem coursework).
i guess if you are disciplined and masochistic, you can simply borrow a friends biochem book and start on page 1... stryer, voet n' voet, and van holden, are popular books to check out.
i found this book called "basic concepts in biochemistry"..it's thin and potentially readable in a summer. (if you are masochistic, again.)
i think you'd be better off partying your butt off now, and save that anxiety-workaholicism for when you actually take the course in school.
goodluck-