I was playing through blood money and I wanted to derp with the game a bit but I noticed that the Steam version has the cheats option disabled.
So I decided to do something about it. With a bit of google searching and doing some debugging myself, I wrote a cheat enabler for the Steam and Retail versions of the game based off of ZoiD's original cheat enabler[forums.eidosgames.com].
All you have to do is run the application while the game is open and then select what version of the game you have. Once you're in actual gameplay, press C and the cheat menu should open.