MCE requires one analog Tuner for (SD). Therefore if you want to add a digital tuner (OTA HD), you will need at least one analog tuner.

If you are in Canada, Microsoft and ATI officially don't support OTA. Therefore, by default, MCE will not recognize the OTA card once you enter a Canadian Postal Code.

I met these guys at the a recent home show in the Toronto area. They just started a forum that is geared specifically for MCE.

http://mcehq.sensuz.com