That particular card will do over the air HDTV, but not cable. In Canada, due to regulatory differences versus the US, you're not going to be able to fully replace the functionality of the digital cable PVR. They lock up those HDTV digital channels pretty tight on this side of the border. There are hacks, but they'd be unreliable and not get you nearly the content you're looking for.
Where do you live? OTA HDTV (ie plug an antenna into the PC) is free and excellent quality, but availibility of signals varies by location quite a bit.