Enter the following codes under the "Extras" screen:
All modes: GM2OPEN8
All teams: A11T3AM5
Streetballer team: 5Y104D9A
Maximum player skills: MAXSKILL
Infinite turbo: SPEEDY01
New object in inventory: E06J3CT5
Weak CPU players: WIMP_A.1
Micro soccer mode: Z26BEXW8