To unlock it all in one go, enter "Nosliw" as your character name. All tracks and cars will now be at your disposal.

Enter "Reki" as a your name.

To unlock cars in a quick race, take a mini cooper or a slow car and use it in the race. Because you have a slower car, your opponents have similarly slower cars as well, and makes the race a little easier.

TT Roadster and TT Coupe: Earn all gold in quick race under easy.
TVR Tuscan Speed Six: Earn 100000 Total Kudos.
Free Roam in Time Attack Mode: Obtain all silvers or golds in Kudos Challenge Mode for one of the four cities. Free Roam will be open for that city. Repeat for each city.

To unlock the Lotus Exige, get 50,000 total Kudos.

The more hours you play, the more helmets you unlock. Every hour you play Project Gotham, you get another.

To earn some nifty new paint jobs, rack up five hours of gameplay. That's it. Just play.

To unlock the Panoz Esperate, get 25,000 Kudos.

To get the Beetle, simply get 1000 Kudos on easy difficulty.