Got bugged up by trying to finish Project IGI2?? Here is a solution..
First to get all the levels, do following in the main menu:
Left Shift+Left Control+F9 simultaneously..(Yes it works!)

Then go to the folder PC/common/ai/ and replace the file named settings.qvm with THIS file. (Keep the original file somewhere else if you want to unable the cheat later)

Now start playing and there...no one yes absolutely none can hurt you anymore including those deadly APCs and choppers!

Kill the enemy at point blank range, enjoy them running around you without realizing your presence..

Enjoy the killl...