Sega Sports Tennis cheats and cheat codes for Playstation 2

Change clothes
Go to the character selection screen, then hold L1 or R1 
and select a character.

Unlock King or Queen as playable character:
Beat all the matches without using a single continues.
If you were playing as a male character, you will face King, if you were 
playing with a female character, you will face Queen. Beat them, 
after they will unlocked.

Special rackets
Play in world tour mode. Beat your opponents in stage 3 and higher 
without losing a single set. If you win, you will receive a 
special racket in all the championship which you won.

Unlock King's Court
Play in world tour mode and beat the Queen and the King also in stage 5.
To unlock Stage 5, you have to win the mixed double match in stage 4.