Thanks for all the replies! I used this tutorial which I tweaked slightly to make my video.
http://www.youtube.com/watch?v=dm1y7i22YF4
What I did was after loading my video into Photoshop, I went to the first frame and saved a shot of just the car as a .png. I then edited the car with the image of the girl. Then I followed the steps in the tutorial but instead of saving as an animated gif, I rendered it as a Quicktime video. You can make awesome special effects using this technique.