Note: This procedure involves editing a registry value; do not attempt this if you are not familiar with working with your system registry, as a mistake can cause serious problems with Windows. Start Regedit and use the "Registry/Export Registry File" menu option to create a backup copy of your original registry. Go to the following entry:

HKEY_LOCAL_MACHINE/Software/Computer Artworks/TheThing/1.0
Create a string value by selecting "Edit/New/String Value" menu option. Name it one of the following "String Value" names and press [Enter]. Right click on the "String Value" name entry that you just created, click "Modify" then type 1 at the "Value Data" field and press [Enter] to activate that code. Note: Replace 1 with a 0 to disable an activated code. Exit and save the modified registry. Note: Cheats will work after a new level is loaded -- loading a saved game will not activate them.

Effect - Registry String Value
Unlimited health for player - PlayerInvulnerable
Unlimited health NPCs - NPCInvulnerable
All weapons - FullWeaponEquip