Unlock The Studio track: 

When the Muppets are racing over the logo, press
Square(2), Circle(2), X, Circle, Triangle, Circle,
Triangle, Square. If you entered the code 
correctly, a message will appear.


Unlock Arches track: 

When the Muppets are racing over the logo, press 
Square, Circle, X, Circle, Square, Triangle, Circle,
X, Circle, Triangle. If you entered the code 
correctly, a message will appear.


Unlock Fraggle Rock track: 

When the Muppets are racing over the logo, press X,
Square, X, Square, X, Square, Triangle, Circle, X, 
Square. If you entered the code correctly, a message
will appear.