I've never been in the Marines but interviews are pretty similar no matter, which company you want to join. They want to make sure that you are right for the job, the job is right for you and you will be a 'good fit' in the company i.e. not be an a$$hole and upset everyone.
There is a short video at
http://officer.marines.com/marine/making_marine_officers/officer_selection_officer
The best advice you can get is to be who you are and be honest about why you want to be a Marine officer. Joining the military isn't like joining a civilian company where, if you don't like it, you can look for another job and leave a month or two later.
I'm assuming they know that you have another 2 years of college so this will more than likely just be a chat about your current situation (studies, personal life, etc.), your reasons for being interested in joining the military rather than a civilian company, etc.
For questions to ask them you should think about things like the interview process, some advice on the qualities that are need to be a Marine officer, anything you can do to improve your chances in being accepted, etc.
The link to the vid I posted seems to place quite a high emphasis on leadership so if you have any experience of organising activities then these are likely to be highly regarded. If not then maybe you can join a club or volunteer somewhere that will help build these skills.
I would say what they are looking for now is a solid interest in being a Marine officer. They know that 2 years is a long time and there is a good chance that your goals will change during that time i.e. you meet a girl and don't want to move away, you get offered a good position in a civilian company, etc.