Brantr

I just got Media Center 2005 and I am new to it. I have a wintv usb tuner and I am not sure if it is compatable. If I have to get a new tuner that is fine, but how do you configure your cable set top box to work with the pvr. For example, If I have a tuner card and want to record a movie on channel 400, how does it know to record that channel? It seems to me you would have to manually set the channel on the set top to get it to work which voids the whole point of the PVR. I could obviously do the non digital channels with no trouble. Sorry for being dumb about this. Thanks