You want to be at GrandCentral Terminal (take train 7 from time square 42nd St station) around 6:30am then take MetroNorth Train to White plain. you will get to white plain station by 7:30am then take cab to Westchester medical center NYMC administration building. You will be arriving by 7:50am. Cab will cost you 12 bucks, a round trip train ticket will cost around 18 bucks.
Good luck. I interviewed there a couple weeks ago, and was really impressed with the school.