So, your ADDING to an existing set up, correct ?
The H25 requires a SWM set up, which you
probably have already, you can check in the System Info if you need to verify .
As mentioned above, I would Call D* first and see what they have to offer, sometimes you'll find adding recvrs is free, most times it not, but it depends on your situation.
Typically they are $100 ...
Solidsignal also is a place you can get and activate D* recvrs ... If D* is $100, thats pretty normal and SS is the same price at the moment.
DIRECTV High Definition MPEG-4 Receiver (H-25) from Solid Signal