At the main menu, go to the Password option and type in any of the following passwords.

Password - Effect

ELDRICK - Unlocks over 20 Golfers and 30 Course Memberships
JUSTDOIT - Get Nike Sponsorship
shojiro - Bridgestone sponsorship
snakeking - Cobra sponsorship
just shafts - Grafalloye sponsorship
gameface - Have all players in team play
inthegame - Level Three EA Sports sponsorship
mactec - Macgregor sponsorship
rihachinrzo - Mizuno sponsorship
jannard - Oakley sponsorship
lightning - PGA tour sponsorship
solheim - Ping sponsorship
guys are good - Precept sponsorship
mr adams - Taylormade sponsorship