Flamdwyn Aiobhell - Unlimited ammo
Monty Barrymore - Unlimited ammo and invulnerability
Lyn Wins - Unlimited ammo, invulnerability, and enables other cheats
Other Cheats:
SHIFT-CTRL-ALT-TAB - Speed warp
ALT-V - No fuel
SHIFT-V - Refuel
ALT-T - Overtorque toggle
CTRL-T - Terrain-following toggle
There you'll find the statements:
infiniteammo=0
invulnerability=0
Now simply change the two 0's into 1's.