See, we can't get Fox in HD through our cable provider because Fox and DirecTV signed some sort of exclusive contract. But the other day I read some article that mentioned that almost every HDTV sold today has an HD tuner built in (by law?), so I checked the manual for mine, and sure enough...! So all I needed to do all this time is plug an ordinary antenna into the input on the back and it would scan the airwaves for both analog an digital stations. We just hadn't even bothered trying that because we assumed we'd need an HD tuner box of some sort and it would be too much hassle just to watch the occasional show.
Of course, we can only watch it live, which feels very abnormal for us, but for the occasional show we can manage. It's really just House and football... but now there's no more football on Fox this season so it's just House. The rest of the Fox shows we watch aren't filmed/animated in HD anyway.
We're also limited to the TV's speakers when using the antenna, which aren't bad at all, but they aren't surround sound. So we're going to get another optical audio cable so we can send the digital audio from the TV to the receiver. This will also solve a problem we have with the HDMI connection between the cable box and the TV. Since we told the cable box to NOT send audio over the HDMI cable and instead send it out the digital coax so it can go straight to the receiver, for some reason this messes up the HDCP handshake and we get snow on the TV until we change stations between an HD and a non-HD signal. Sending the audio through the TV will get rid of that annoyance.