No problemo...not many people know about PBM's, I'm probably one of the few that have rotated into that on SDN (if you're out there...hellooo).
Medical Information within the industry is basically like the drug information arm of a pharmaceutical company. Everytime a brand drug is marketed/released, there's a whole team behind it that supports it--everyone from drug reps to people doing post-marketing surveillance, etc... One of those support functions is medical information -- anytime a rep can't answer a question (either it's too clinically deep or not a labeled indication,) they have to escalate it up. OR if a practitioner initiates a question about a new study for a drug and wants some more information. There's other functions too (like helping train other staff in new drugs, etc...).
You being at Rutgers...you are smack in the middle of industry, I'm sure you'll have opportunities to rotate into a pharm company at some point. If you can, do it just to see.
Okay your 1st set of questions about getting hired and/or internships -- I can't really answer, it all depends on the company. Like any place to work, it would be difficult to get a job without knowing anyone there. If you rotate in, that serves as a de facto interview/trial period and I've seen this happen many places (including PBM's). Once you're hired, no matter if you are "fresh," rotated in, or were a resident there/somewhere else.... you wouldn't be at a disadvantage knowledge-wise (for long, anyway). It might take you an extra week or two to learn the computer systems, workflow, and culture, but really the hard part is getting hired in the first place...so work on your networking & maximize your experiences/face-to-face contact.
2nd set of questions -- I'm in rotations now, so I won't graduate until 2012. My advice for you is to try to find a hospital internship job unless you're 100% sure you want to work at CVS. They'll probably jettison you anyway if you don't sign a contract with them later on. Retail intern jobs, IMO, are only good if you're planning to be retail-for-life. Hospital jobs look a little sexier on your CV and open you up to more/wider opportunities later on, ESPECIALLY if you're wanting to work in a non-retail environment where many of pharmacists either hated/escaped retail or have some sort of disdain (YMMV -- some pharmacists love retail, so try not to trash talk too much).
Other advice -- get involved, but not too involved, with organizations... and try to do some research/present some posters at ASHP.
My background, if you had other questions: CVS for 1yr pre-pharmacy, 2 years inpatient intern, 2 posters, minimal org involvement, undecided on pursuing residency/career path...except no to retail