Calling all Xbox 360 owners with Live Subscription,
To claim your 500 Microsoft Points, all you have to do is register on this web site using your Windows Live ID associated to your gamertag.
You can register until midnight (Pacific Time) on November 29, 2007, and after you do so, you will receive an e-mail with a 25-digit code that lets you activate your Microsoft Points through your Xbox 360 console.
Don't expect that email to arrive instantly as the deadline for that email is December 21, 2007.
Xbox Live is 5IVE: How to Get the Free 500 MS Points - Xbox