Buying a 2003 accord this weekend need help!!!

Ok my cousin is buying her first new car she just turned 23. She already picked out and test drove what she wants a 2003 Accord Lx. The sticker on the car is $20,010. This weekend honda is offering 0% APR so she is goin to be purching the car. What price should we pay for this car and how do we deal about getting that price. I have never bought a car from a new car dealer.....being only 16 i have bought my first car from a private party. We both just moved to the area and no one eles who could help us out on this. I know from common since that if we are fleixable on colors and certain options that that should help our case. Please some one tell me what to do we need to do it this weekend and we dont want to get ripped off. thanks
ryan

Start by checking www.kbb.com( Kelly Blue Book) and www.edmunds.com or any other car site for new car buying guide.
Good Luck...sickhonda