This tip is only valid if you have pre-registered, and been sent 2 emails (1 saying thanks for pre-registering, 1 saying your new box is ready).
The website isn't working, and apparently there is a required reference number missing as well.
The workaround: Call 01506 677005
Select Existing customer, sky hd and sky plus, sky HD (I think those are the menu options)
Explain that the website isn't working, give account number, they can see if you have received the second email, and will put the order through. YOU MUST REQUEST THE 1 MONTH FREE HD PACK, otherwise you won't get it. Explain that you know its only available online, but the website isn't working.
Note: If you start the process online there is nothing CS can do, so if the website dies halfway through, you are knackered. They can only help if you haven't let gone through the online bit.
Hope this helps someone. I got my install date for next week and the CS rep said I was the first to take the offer by phone. There was lots of hold time, and apparently there are now meetings going on because the emails were meant to have a reference number and don't.