If you have read the code above this and tried it but

A.you dont have a game cube

B.you DO have a game cube but no LOTR:ROTK game

C.you dont have a link cable

Then try this

1.be Frodo in new game
2.get up to the level where you play as sam(i think it's Shelob but im not sure)
3.save

Thats it! now go to any Bonus/Multiplayer map and you can be good ol' Sammy

P.S you cant be sam in single player

P.P.S to be him in Bonus maps you must have at least one empty save file

Hope that helped