couldnt be any simplar, load resistance up, start story, when you are able to move, press start save and exit, highlight yes, eject the disc and insert MW2... check it says MW2 by pressing the ps button and looking under the game section, press the ps button and click yes this should load up mw2 no you ned to go online and then go splitscreen and make two more profile these are the profile you will load error into one and the prestige into the other. once you have mad the profiles quit the game edit the saves, and restart the process.. but this time in split screen load the error file, then go back into splitscreen and carry on and prestige, then go back and load the prestige file and back out again, then go to online and prestige there.
for a full tutorial look at the mw2 prestige hack thread. hope it clears a few things up