Without seing the photos, I can only assume how this was done.
Generally, an untouched (as in original) photo wont have these trails. It is possible to get light trails in photos, but from your description, it sounds like the whole car is blurring behind.
When you take a photo of a car in motion, and to capture the motion, you need the shutter speed open for slightly longer than you would normally do. A fast shutter speed will snap the action, and freeze the background. The only true way to blur the background and keep the car sharp is a technique called panning. This is where you leave the shutter open a bit longer, and follow the car. If you manage to pull it off (its tricky) then the car will be pin sharp and the background will blur. This is because, as far as the camera was concerned, the car stayed in the same part of the lens, while the background moved. Such as this photo:
[You must be registered and logged in to see this image.]As you can see, there are no trails behind the car.
If there are trails behind the car, then its likely been photoshopped. The most common way to do this is to seperate the car and background in photoshop, and motion blur the background. Because the car is excluded, it stays sharp, but parts of it will be used by the computer to generate the blur. It basically takes the whole picture, and smudges it to the right slightly. You will end up with an effect like this:
[You must be registered and logged in to see this image.]Its generally frowned upon by pro photographers, but its a way of adding more motion to a photo when you failed to capture it at the time you took the photo, or to increase the illusion of speed.
Its also possible to take a completely static image like this parked car:
[You must be registered and logged in to see this image.]and do the same effect using the above techniques in photoshop
[You must be registered and logged in to see this image.]To the unsuspecting, you might think it was a photo of marcus in full flight, but no matter how good you are at photoshop, there are always tell tale signs that its been altered.
The best thing to do, is practice, practice and practice until you can nail a panning shot.