It's a classic pyramid scheme. You have to get 3 people to enter their email address at each level, sounds easy right. Lets first take the most basic a PSP memory card, you need to get 3 people, they in turn need 3 people and they then in tern need 3 people.
3 x 3 x 3 = 27 people
But I'm sure you don't want a PSP memory card?
Xbox Elite - 3^15 so
3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 = 14,348,907
So all you need to do to get an X-box is to get just over 14 million people to sign up.
Good luck in getting 27 people to enter their email address into a system so YOU can get somethign out of it.