All Tracks and All Vehicles-First you need 2 controllers plugged in. I've made steps to do this
1. Turn on the game and press start on controller 1 until it says to press star(If you see Grand Prix Mode you've gone too far)
2.On controller 2 press up on D-pad+C-Down+R+L+Z and release.
3.Immediately press Start or A on controller 1 to enter Grand Prix Mode.All Tracks and cars Should be available(in all modes)It takes patience so don't give up the first time if you do it wrong.

China Town Jam Track-race in grand prix with the difficulty set to EXPERT. Beat the game with a first place ranking on each course and the new track availible.

Drive the N64 Controller-This Strange hidden bonus vehicle in availible by choosing the time attack mode. If you get a race time that ends in a point zero six four(.064)It will be availible.Cool huh!

Finish the game in First with the....
Black Lightning to get the Dominator
The Hornet Car to get the Prowler
Shredder Car to get the Reaper
Avenger to get the Vengeance

Neo Speed Way Track-Beat The game with first place ranking on INTERMEDIATE to get the Neo Speed Way Track.

Tip:Turbo One of the essential tricks to win tracks is the Turbo Boost. Hold down the A button during the race and drift hard left or hard right holding Z. Let go of both buttons and you will get a nice little boost. Practice the boost until you can do it perfectly,now you should be able to win without a problem.

Extra Track And Vehicles-To do this trick you must have 2 controllers. Using controller 2 go to the title screen. Press and hold R+L+Z+C down and up on the D-pad then release them all. Next, press the start button on controller 1. The extra track and vehicles will now be at the track and car select. Note:This may take a few times