No, you don't actually get to win the Iron Throne (cool as that would be). The grand prize winner does get $10,000, however. Which is probably enough to commission a local ironworker to make you your own Iron Throne, if that's what you want.
There are also all sorts of lesser prizes for the runners-up, in the form of GAME OF THRONES swag.
Sorry, the contest is only open to US residents.