I'm not sure what kind of position this is but especially if it's professional, post-grad....
Do research on the company. Visit their website or find other info about them. One thing my manager is always impressed with is a knowledgeable applicant. It shows that you really are interested in the company!
Bring extra copies of your resume (on nice resume paper). They might not have your resume right there with them and it might be helpful to them (if they don't have it) to keep another copy or use it as a reference point in the interview. I know that on several interviews last year I needed extra copies for HR, etc.
Have a list of questions (maybe 3 or 4) that you would like to ask the interviewer. They will typically ask if you have any questions atthe end of the interview. Having a list (in your head) again shows that you are prepared and have put thought into the interview. You will know what is appropriate based on the type of job you are seeking.
You might want to check out a book about interviewing. I know it sounds cheesy but I checked out a book from the library last year when I was interviewing since it was really the first time I had done this (for a professional, post grad position). I think I got "The Interview Book" but there will be several to choose from. These books will provide sample questions that will probably be asked of you and will also give you some sample questions that might be appropriate to ask the interviewer. For the sample questions, don't psyc. yourself out but it is a good idea to start thinking about some of the answers in advance. You don't want to sound "rehearsed" but you'll want to know a general direction in which to go. Things like "where do you see yourself 5 years from now", "How would you handle a conflict w/another employee", etc. Give concrete responses if you can...it's much better to illustrate how to handle something then speaking in the abstract (at least from the interviews that I've helped conduct).
Wear a suit if you have one (you can never be "overdressed"), keep the makeup and hair simple yet professional. Get a good night's sleep the night before and RELAX.
I'm sure you will do wonderfully on your interview. Let us know how it goes!