I have a DirecTV HD-DVR with USB ports and it unfortunately does not work like this. To do so, it would require a lot of different CODECs to be in the cable box and since they are not built with this functionality in mind, I'm fairly certain it won't work. The PS3 makes it possible because Sony has a lot of the CODECs built in and they've been pretty good about releasing new CODECs over time to address any that change or are missing.

Jason

Epic 80-800: HG Cherry