Enter these codes at the ENTER CHEAT menu option, I do not know if these cheat codes will work with the PC version as that version has not yet been released.
1) All characters in Multiplayer Mode To enable all characters in multiplayer mode, enter the password OMGTKKYB
2) All Weapsons For all weapons, enter the password FATKNACKER
3) Big Head Mode For big head mode enter the password MEGANOGGIN
4) Invincibility For god mode enter the password ASSMAN
5) Level Select To chose your starting level enter the password THEEARTHMOVED
6) Master Cheat I'm not sire what this does, but the password is BOBBYBIRD
7) Pen and Ink Mode For Turok's famous "pen and ink mode" enter the password PLANEARIUM
8) Unlimited Ammo For unlimited amo, enter the password FATTERKNACKER
9) View Credits To view the credits, enter the password screwyouguys
10) Bonus Characters To access these characters in multiplayer mode, enter one of the passwords:
veggieheaven = Skinny cheatingisbad = Mr.Mackey elvislives = Bar Brady outrage = Big Gay Al hawking = Ned slapupmeal = Starvin Marvin phaert = Phillip raft = Terrance dorthysfriend = Mr.Garrison lovemachine = Chef checkataco = Wendy Testaburger fishnchips = Pip kickme = Ike allwoman = Mrs.Cartman goodscience = Mephisto staringfrog = Jimbo majestic = Alien niceoffice = The Mayor