The GU interview had 4-5 people in the room (various professors, plus a rep from WHC who also teaches at GU there too). The WHC interview was 1-on-1. The questions were very similar between the two, and very basic - just a review of my background. Yes, they had my full application on hand (plus the essay for the WHC interview). It was very clear that they'd combed through my background pretty well. Questions about any sub-par grades; questions about time off; questions about how you would apply skills from your previous background; questions about the activities you're involved in -- are all fair game, and pretty standard for any job/school interview.
Make sure you have a good answer for why you HAVE to be a nurse, why you HAVE to be at G'town, and make sure you can address any obvious weaknesses. For WHC, they want to make sure that you really want to work in an urban hospital setting, not just get a scholarship.
They're also looking for a well-rounded pool of students, so the more 'diversity' you can add (gender, age, race, foreign languages, etc) the better. Both interviews were pretty quick - WHC was harder just because it was at the end of the day and everyone was pretty tired. Pick up a business card from your WHC interviewer & make sure to send a thank you. Smile, relax, and try to have fun with it. Good luck!!