c# key press please some one must know

Question

basicly iv made a trainer for a game in c# does every think all the buttons work and that only problem is the keydown option only works when form selected and i need to know a way of the trainer finding every key press that comes in weather form selected or not

since it wont be selected because the game halo2 will be full screen if you could show me a way to do this i will be most greatful

how ever im not that good of a developer so please keep the answer minimal in the sense i dont want pages of code where half of it is not needed