2 ways to go, first a receiver with embedded cams where you update the embedded cam with a computer + RS232 cable and update the key codes with the receivers remote control, great as long as the receiver and computer are in reach of each other.
Secondly a receiver + cam + cas2 interface, with this system you update a cam plugged into the cas 2 interface which is in turn coupled to the computer via USB port and update the key codes via the remote as before.
A cam is a device which de-scrabbles the providers encrytion so you can view the channels. A cas2 interface is a device which enables you to write new software onto the cam. A key code, putting it simply is a row of numbers which is changed by the providers every so often, which you can change to suit, very simply with the receivers remote control.
I prefer to use external cams because major changes to software seem to be more readily available. Several different cams are about, I prefer matrix revolution myself, so best you ask around before making up your mind.