I think he wants something a bit beyond that: a tuner card PLUS software to descramble encrypted cable broadcasts, which use an algorithm like Videoscrypt or Newscrypt.
This is definite hacker territory and if you want to learn more, do a Google search on "hVCPlus" or "hNCPlus".
As far as I know, there is no Mac version, and you can hardly ask a company to make one, as the authors of these programs live way underground!
They're open source though, so maybe one day they'll be adapted for the Mac OS. For now, if you want to rip off cable, you'll have to have an XP box.