It isn't easy, that is the first thing I will say. Don't think you are going to make a grand RPG or some amazing FPS, because large companies make them, almost impossible for one person to do it.
Think small, addictive and smart. Small games that are addictive are good places to start. Look for tutorials online. Riemers is a good place to start.
Well, what is stopping you from downloading Visual Studios and XNA?
Those are what you need to make games for the 360. Best thing I say you could do is start learning it. If you pump out a game or something original, you can get head hunted like that, grades or not! :3