The box you're refering to is an Amstrad DRX890- It's being trialled by Sky staff and a small number of subscribers at the moment.
AFAIK,there is no confirmed date as to when it will be officially launched, just rumoured to be "early 2010".
As for ensuring you get one,well you cant.Sky cant/wont guarantee you a choice of Sky box,you get whatever make the installer happens to be carrying on his van at the time!