I couldn't get god mode to work at all, but it's really not neccessary on this game. You're really in no danger of dying except for the last 2 missions.
The end level cheat is the real gem here. It worked flawlessly and I was able to get Blitzkreig and beating the game on Agent achievements in about 2 mins after following swagger's guide for the other 43 achievements.
If you don't have a USB keyboard and just a standard PS/2 keyboard, get this from Radioshack:
This is what I used and it works perfectly. Well worth the $20.