Unlockable Cheats
Cheats appear in the Specials menu and the buttons are repsective to your version of Tombraider Legend. Cheats are only unlocked when you clear the game or meet the following criteria.

Textureless Cheat ... Clear the game (any difficulty).
Show enemy health ... Clear Bolivia under 12:30 in Time Trials.
Infinite MG415 Ammo ... Clear Peru under 21:30 in Time Trials.
Infinite RC650 Ammo ... Clear Japan under 12:15 in Time Trials.
Infinite shotgun Ammo ... Clear Ghana under 20:00 in Time Trials.
Infinite grenade launcher ... Clear Kazakhstan under 27:10 in Time Trials.
Bulletproof Lara ... clear England under 27:00 in Time Trials.
One hit deaths ... Clear Bolivia (stage 8) under 4:15 in Time Trials.
Unlock Excalibur ... Clear Nepal under 13:40 in Time Trials.
Unlock the Soul Reaver ... Clear the game and complete all time trials.