At  the  beginning, the game opens up with a menu (single player,
multi  player,  etc.).  Go  to  "Options",  choose "Cheats." Enter the
cheat, and press enter.

Code                       Result 
MR HAPPY                   No Dressage Failures 
BIGHEAD                    Big Head Mode 
PHAR LAP                   Unlimited Energy Round the Cross Country 
CHRISTMAS SNOW             You'll See 
GENIE IN A BOTTLE          Unlock All Tracks & Horses 
NEW YEARS EVE              Fireworks 
TANTALUS BIG AIR           Ballistic Rider