Easily earn a 1600 Microsoft points code for free at Points2shop.com by registering and getting 2000 credits on the website and they'll buy you a code free of charge. Theirs many ways you can accomplish earning the 2000 credits and I'm going to show you the fastest and easiest ways possible.
One of the methods to get credits is referrals. Referrals are people that you get to sign up at Points2shop using the special referral link that they give you, You'll earn 100 credits per active person that you bring to their website. Since your probably already a member of Xbox live you can use that for a place to put your referral link.
Add the ref link to your Xbox live profile explaining how they can earn prizes, so every time you play a match online and your ripping heads in MW3, winning a race in your favorite racing game, or if your high ranked on some leader board for the game or games you play. People online can see your profile an they might join the website with your link earning you automatic credits just for playing Xbox live.
Use your Xbox live friends list as a place to get the word out about the website, just tell them about the freebie website and how you got or how your earning your 1600 Microsoft points code for free at Points2shop an give them your link so they can sign up under you.
If you don't think you can get a referrals for the website, don't worry its not the only way to gain credits! You'll see the website is set up for you to easily get a code free without doing that. They have surveys, games, and offers for anyone that doesn't want to be bothered by referring. In my opinion its best to do them all because your credits will keep racking up over time, but they'll all work so its 100% up to you how you earn them.