Ok, to give you an idea, Here's a picture I found, the first is befor and the last is after. The second pic is the steps in between

1Start by cutting out the car, and pasting it as a separate layer

2 you can't just blur the background or the fuzzy white edges will show through

3 So you have to fill in the edges with some surrounding picture - I filled in the entire area, but you don't have to, just the edges will do.

4 Now you can add a motion blur filter

5 Next, I pasted on a layer of the car, blurred it, and erased the front half.

6 then I pasted the original image.

In the final pic, you can see that I added a radial blur to the wheels, and just a slight motion blur to the car.

Voila!