Get Ѕky to send you a new HD box for free
Theres no such thing as free with Sky, theres always a catch, which will probably be in the form of a 12 month contract with telephone connection.
I would check first before going down the route with Sky.
You need to find out if your going to be signed up for another 12 months and more importantly if your going to have to be connected to the phoneline for another 12 months. By connecting the box to the phone line they get a subsidy so you don't have to pay the full price for the box (Apparently)
If your box is not connected to the phoneline when its supposed to Sky will get narky quite quickly and demand you reconnect it. The second you put the card which has been in your 500HD back in the Sky box and it rings home they have got you. Its either breach of contract by using non proprietry equipment or Fraud for CS.
A second hand box off ebay takes away all that issue as they cannot force you to connect that box to the phone (As long as you don't have multiroom) as they have not had to subsidise the box or send one of their monkeys around to fit it, so in theory you owe them knob all
All they have to do is pair the card to the new box
Just bare all this in mind before you order a new box from Sky.
Nano