i messed up

i'm saving up money for the 08 accord and have already decided that i want the lx-premium with certain accessories, only problem is that i will only have about 15000 by the end of 2010. My plan was to buy a used one the way i wanted it, and try to haggle the price down and then give a huge down payment so my monthly payments aren't that big. so does anyone know how much the price will go down?and how should i go about buying this car?*i have already made my mind up that this is the car that i want fyialso i'm about to get my credit card soon and i plan to have as perfect credit as i can get it within time to buy the car.What exactly does credit do with buying a car?i can't afford it now