You should only be cracking the case on the 722 if it is owned. Even then, the internal drive's hardware ID has to be one on a short list of drives supported in the 722K firmware and is limited to 500GB as far as I know.
NR2D, It is not advised that you open the case of the 722k as this will void any product warranty from Dish or the manufacturer. External USB hard drives of up to 2TB capacity are supported. There is no extra charge to connect an external hard drive to the 722k.
There have been reports of customers connecting a powered USB hub to their receivers, but this is not currently supported by Dish.