Dude, your parents need to learn that you're not a kid anymore. My parents don't care what I play, and they've never cared.
As for Halo, it originally was a T rated game. If you look at the ads for Halo in game magazines before it was released, they say rated T. If you don't believe me, I can try to find it and scan it for you.
Then again, Halo is a very light M rated game. There's no violent ways to kill people like in Manhunt or Postal. Blood is minimal, and there's no nudity.
Wrong. Conker's Bad Fur Day for the Nintendo 64.