What is the job insfrastructure of academic journals?

the only real knowledge i have of this comes from listening to a few radio shows who make great on air use and mention of their interns (unpaid students getting college credit for work), they seem to be evaluated as the job goes on, start with basic tasks and see how they progress, some get airtime and do great production pieces, some seem to spend their entire time getting breakfast and coffee for the hosts and guests

Have you picked a journal? Just approach them. I'm guessing you might be able to pickup volunteer work in citation checking, maybe even proofing. Editing and layout will still be mostly in the hands of paid professionals. But it does depend on the journal. Open access titles might be a better bet if you want more varied dirt on your hands. Are you attached to an institution with an academic publishing wing?

Book reviewing is always option too.