All tracks and such:

At the password screen, enter C9P5AU8NAA to unlock every track, legend and car through the pro level.

Unlock Everything:

At the password screen, enter KMZWA8AWAA. This unlocks all secrets on the game.

Find the Wrenches To Access Hidden Cars:

-Chicken truck:

The wrench for this car is found in a chicken hut on the "Fowl Play" stage

Sprint Car:

The wrench for his car is on the last shortcut on the 'Dog Tired' stage, turn left at the track and there it is.

Jet Car:

Located on Bad Lands, set on Stony Creek. On the last turn of the track hit the jump, going left and you should land on a short cut. Turn around and head back towards the end of the short cut and the wrench is right there in front of you.

Unlock The EA Sports Car:

Beat EA Tournament in Rookie mode and you will unlock the EA Sports Car in Rookie mode. Then beat the game on Pro and you will be able to race the EA Sports car on Pro. It is the same for elite.

Access More Hidden Cars:

On the stage Hog Hollow near the end of the course there is a building that looks like a gas station. You can drive behind it so go slow and there should be a shed go to the front and hit the light brown door it should appear in front of you.

Golf Cart:

Located in Mardi Gras on Big Easy in the middle of the track take a shortcut right through a house. Go to the last room and turn right at the bookshelf. Break the wall and the wrench is in front of you.