Select head to head mode, pick your car, and right after you pick your opponent's car press and hold up-left on the D-pad, L1, square, and circle until the race starts.
Result: machine guns
note: press up for the machine guns
Go to the password screen and put in the password: SPKSHC , pick your car, then go to Rusty Springs and hold L1,R1, and, triangle
Result: A secret track , called lunar springs