Unlock All boxing boards:
Enter "NEWVIEW" in the create champ mode as the first name, after save

 
Full Stats:
Enter "Mr. Skitz" as character name
 

Unlock Ko Rey Mo:
Beat him in career mode under the light heavy division

Unlock Staple's Centre venue:
Win at the Staple's Centre in career mode

Unlock Madison Square Garden Venue:
Beat a match at the Madison Square Garden Venue

Unlock Boxing styles:
Win Joe Frazier with Ali - Judge Jab

Win a Classic fight with Roberto Duran - Lethal Uppercuts

Win a Classic fight with Roy Jones Jr. - Sinister Cross

Win a Classic fight with James Toney - Slickster

Win a Classic fight with De La Hoya - Textbook

Win a Classic fight with Winky Wright - Uptight, and Hard Straights

Burger King as your trainer:
Win the Burger King event in Career mode. Aftet that, while you are at
the train selection screen, press DOWN until The Burger King appears 
as selectable. Note: He gives you Heart when you fight.