I just got accepted into the University of Arizona's RN-BSN program for Fall 2008. Consider yourself lucky to have the interview opportunity--I know it's nerve-wracking, but it's the best chance you get to sell yourself. At the UofA, all we got was a 250 word personal statement. It was quite a bit of pressure to sound amazing on a (small) piece of paper.
One thing that helped me out a lot was going in to bug the nursing advisors. I went in there and asked about EVERYTHING, no matter how stupid my questions sounded (and trust me...there were some good ones). Basically I did this for the purpose of exposure...by the time I applied, the members on the admission board all knew me by name and face. This is GOOD. I might not have gotten to interview, but in the end, it didn't matter.
Basically, every admission board member will tell you the same thing. Stand out. If they don't remember you, they won't pick you. Make your personal statement a piece of creative writing (while still being professional and answering the question, of course). Don't write the boring way we all think admissions boards want to read (they don't--would you?) Make it INTERESTING. Assert yourself. Don't say "if" I get in, say "when" I get in. If you believe you, they will too.