You need the PS3 SDK (aka PS3 Software Development Kit). I'm afraid it costs money. If Sony aren't tards you probably can download a demo version or maybe a personal version.
Then you of course need to gain programming experience.
And finally you'll spend 1 year designing the game, 1 year programming it, and 1 year making the graphics. That if you have a team of atleast 10 developers. Well and then success, you now made Modern Warfare 3. But oh well? Copyright issues? Oh gawd you didn't know of that, but well it was fun as long it lasted, now too bad you had to pay your billion income to Infinity Ward.