As stated by others cable stream all the channels (even the on demand streams other people in your area are viewing are streamed to your box) and they are encrypted (by nagravision) so to decrypt them you still need the viewing card, and just getting a DVB-C card with a CAM to take the card wont be sufficient as the viewing cards are locked to the mac of the set top box.
There are ways around it with software CAM emulation, but it's very much against the Virgin t&c's and on very dubious legal ground.
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Cable...
As stated by others cable stream all the channels (even the on demand streams other people in your area are viewing are streamed to your box) and they are encrypted (by nagravision) so to decrypt them you still need the viewing card, and just getting a DVB-C card with a CAM to take the card wont be sufficient as the viewing cards are locked to the mac of the set top box.
There are ways around it with software CAM emulation, but it's very much against the Virgin t&c's and on very dubious legal ground.