The DTC-100 cannot enable firmware upgrade by "card." Upgrades are only available via satellite. What many are doing is finding someone in their locality with a DBS dish for DirecTV and just hooking up the DTC-100. One night should do it.
Good luck.
For whatever it's worth, imho progressive scan, annamorphically-enhanced DVD is so close to equal resolution with most HBO HD movies, that it's a virtual wash. The HD will always be just a wee bit sharper, but the difference is minute, and the 5.1 or DTS audio available via DVD really tips it...
I called my local CBS and NBC affiliates and got the news they aren't expecting to be up on HDTV until Spring of next year! But they will be full power then, not running a low-power station like many are at present.
This points up to me, again, the utter folly of OTA HD broadcasting. Sure...