I'm in the Info Systems track at my school, and a paid Web Developer apprenticeship opened which I applied for and was accepted. Currently I only have (minimal) Java experience. The company understands we are students, and don't know anything for the most part. We will be using Rails as our primary language... anything I should expect, and do in my week to prep other than obviously familiarizing myself with RoR?

Email your employer and ask. They should be able to help you out with something useful to do.

If the company's small, work on your customer service. A small company will likely have you speaking directly with clients, or would really appreciate if they could have you speak directly with clients.

It's easy to be a proficient coder/designer. Something I have always found impressed smaller companies I have worked for is my ability to handle clients myself.

Edit: I realize you were probably asking for coding specific advice but that's hard to say what different companies would expect.

Since this has been relevant to pretty much all the students I know (including myself back in the day)...

Find out what version control and other software development relevant stuff they use and get familiar/comfortable with that.
This includes preferred operating systems btw. seen quite a few people that have used Windows all their life kind of surprised when they started at a Linuxy shop and where implicitly expected to know their way around typical Linux stuff
This also includes testing, find out if they do TDD etc., find out what the development process is like (Agile etc.)
tl;dr: Most students tend to be spaghetti-coders that know only one environment well and don't use any form of project management. That's perfectly fine and the biggest value of your first programming internship is picking up all this stuff imo

Obviously get a grasp on RoR, do the tutorial and some small project (mostly to see how often you have to refer back to the tutorial). Get comfortable with finding RoR/Ruby information quickly. Can't hurt to also refresh the other webdev related skills (HTML,CSS,JS+SQL...well guess figure out if they use an SQL-DB first)

Most importantly don't stress out.

So yeah write an "hi, I want to prepare for my internship" type of email where you get answers to most of these questions and prepare accordingly.