This is retarded.
Interest? Don't charge a minor purchase you can't pay off immediately. You don't have a 750 beacon -- if you did, you'd know enough that not only could you get the cash advance, back it up with actual money, but also not pay an outlandish percentage on the cash advance balance (because you wouldn't carry the balance anyway, or you'd balance transfer it to a reasonable-rate card.)
Thread is a crock. And don't buy W7 anyway, especially not from someone who doesn't have a friggin' bank account..