Here is a video of howto do it http://www.youtube.com/watch?v=EWQhlmJTMzw
If you want to buy, a good UHF antenna, the DB4 works for most people and is not expensive. http://www.amazon.com/Antennas-Direct-DB4-Directional-Antenna/dp/B000EHYG9K
The distressing thing was how much better the picture looked off the antenna compared to the cable.
Buy an amplifier for the antenna to get the most out of it. I was able to triple the number of digital stations I could pull in. Install it right at the antenna if you decide to split the signal to different TVs.
If you have an antenna now, the same one will most likely work for HD. But out on the fringe, you might have to experiment some to get good reception, especially in the hills & valleys or in a concrete jungle. The way you will be impacted by or can take advantage of things such as multipath, reflected signals, knife edge diffraction and so on will be a bit different, because with DTV you generally won't have instant visual feedback when you are experimenting with antenna positioning and orientation.
But there is no special magic in HDTV antennas. The common split boom design, with a sort of log periodic section for VHF, and corner reflector Yagi section for UHF, is still the norm - and the farther out you are, the bigger and more directional you will need to go.
In my location there are 6 local stations broadcasting 11 or 12 separate channels of programming from two locations - nearby hilltops that are about 110 degrees apart with respect to my location. The hill to the South is line of sight and also the closer of the two, but the hill to the NE is blocked from view by a thicket of large trees. My small directional antenna is aimed straight at the NE site through the trees, and I pick up the South site off the side. I didn't change a thing when I bought my digital TV a year ago - I just plugged it in and began enjoying more channels and a crystal clear picture on all - and for most it's just that simple.
Tarpon is also right about OTA DTV being superior to cable - and it's likely to remain that way unless and until cable starts delivering by fiber direct to your house. I'm not up to date on satellite tech, it may have similar limitations.
In September, I had a Winegard HD-7084P VHF/UHF Antenna installed. [97.00 from Summit Source]
I get 51 HD channels.
I also have a Sony RDR-VXD655 VHS DVD Recorder Combo with Built In HD Tuner which works great.
later