I apologize for the delay in replying, but we just finished exams. Woo hoo! My personal suggestion would be to scroll through my links page. I haven't checked there for a while, but I *think* there might be a site or two that has help for the essay.
If not, my recommendation is to compile a list in point form of all the accomplishments, awards, scholarships, bursaries, jobs, languages, and extra-curricular activites you've achieved to this point. For the introduction, you'll then be looking for a way to lead into all of these characteristics, and why you believe they will help you become a good doctor. I think is is the point at which you are stuck. I always hated writing the introductions to my essays as well.
One possibility might be to elaborate on your desire to study medicine. Following that statement, use a few creative sentences (ie. not a plain, boring list) to describe briefly some of the characteristics and achievements that you believe are especially relevant. Then, in the following body paragraphs, go on to discuss those qualities in greater detail. That's just a personal idea. Good luck!