If you want ALL cars, you have to do it time and again.
If you want to get one specific car, run at least 6 races out of ten being first / at least 3 out of 5 being first and then simply save at the end.
Just start and outrun all the cars and just at the moment you are 1st, quit and save (NEVER SAVE THE LAST RACE i.e. 5th or 10th race) Thus you will prevent the other guys getting 10 points and they will NEVER catch you. At the final screen after you get your award money, try and locate the silhouette of the desired car and hit X when the circle is under it. If you cannot get it, reset it and redo the last stage as described above...
However,keep in mind that this method will decrease your win percentage.
I hope this has been clear enough.
