The only way to get all the cars is to start ur career with the Name 'BIG' and ur team name 'HEAD'. That is the only way to get all the cars in Need For Speed.
Avoid Getting Busted
Use the following trick when you are in a cop chase and the police have you pinned against a wall and you cannot seem to escape quickly. Press Select to get into the center of the street. Drive off as fast as you can to make the bust meter go down. Be careful when doing this in higher levels; the bust meter fills up a lot quicker and you must be very quick with what you do.
Cars
Defeat the indicated Boss to unlock the corresponding car.
911 Carrera S: MK
Aston Martin Db9: Jenna
Carrera GT and Lamborghini Gallardo: Clutch
Chevy Cobalt SS and Vw Golf GTI: Marcus
Chrysler 300 and Pontiac GTO: Layla 1
Firebird, Toyota MR2 and '67 Mustang: Poorboy
Lotus Elise and Mustang GT: Steve
Mercedes SL65, Corvette and Ford GT: Scotty
Mitsubishi Eclipse: Sly
Nissan 350z: Daemon
Pontiac Solstice: Striker
RX-7, Skyline GTR and WRX STI: Buddy
RX-8, Toyota Supra and Audi TT: Layla 3
Drive On Horizon
When you are at high speeds and take turns that the game would not expect you to do, you will you ride on a horizon. It is all black and slightly orange. Be careful, as you can still crash. It seems like your car is going so fast that the map area was not mapped. This usually happens on the last sprint for Ex on the last piece of territory.
First play?
You should buy the evo. Then do not buy any car until your evo has reached the max upgrade. Then buy the RX 8 and continue, this helps to save money.
The easiest way to avoid getting busted
The way I know it the only way to get the police on your trail is to go Free Roaming. Before you go free roaming save the game, when the police catches you just press the 'HOME' button if you are get busted.
Unlock Everything
At start menu press X, X, Right, Left, Square, Up, Down.
Your Favorite Car
Begin a race in Quick Race mode and select the car you want to unlock. Start the race, but quit before finishing it and save your game. Now load your save file and head to Career mode. You'll find the car available, though you still have to buy it from there.