Undergrad biochem definitely helps.
The difference between the two is that in undergrad biochem you're focusing on generalized biochemical principals. This can be really helpful in medical when you're talking about concepts like enzyme kinetics or thermodynamics. In my undergrad biochem class we spent like a week or two doing enzyme kinetics. In medical school we spent like one lecture. Before this freaks you out, realize that what we talked about in the med school lecture was more of the overview of kinetics (they taught enough to understand why things like why its important that the Km of glucokinase is much higher that hexokinase). In undergrad biochem we were doing complex calculations and using graph paper to graph out rate vs. substrate concentration.
To sum what I just said up most of the things you cover in undergrad biochem aren't really specific to just humans, but are commons traits most living organisms share.
In Medical biochemistry, you're focusing on the biochemical pathways that occur in specifically humans -- plus all the common errors/deficiencies you may encounter in practice. It moves significantly quicker, but its definitely do-able if you put keep up with the lecture (I'm a lecture behind right now so I'll know what I'll be doing tomorrow). Its way more conceptual than anatomy, which, at least in my opinion, makes it more enjoyable.