Hydro Thunder cheats, and Codes for PSX.
Highlight the "Memory Card" option and press R1, R2, Circle, R2, R1. You will hear a sound if you entered the code correctly.
Enter the options screen, highlight "Back", then press Up (x2), Down, Up, Down (x2), Start.
Hold X immediately after the announcer says "one" at the start of the race. In about three seconds a voice should say "Super Start". This allows you to go faster from the start and usually takes you to about 13th place immediately.