Tom Clancy's Splinter Cell Cheats

Link the Game Boy Advance to the GameCube version of Splinter Cell to unlock five bonus levels.
Alternately, complete the normal levels in the game with a high percentage rank (over 60%) to unlock the various bonus levels.
To unlock a sixth bonus level, make sure all the safes are open when playing normal missions 1 through 9.

Unlock the first bonus mission by beating levels one to five with a completion rate of 60% or higher. Get another bonus mission by finding all the safes in missions one through nine.