I use a MyHD MDP-130 and it works great. It's my only option because I only have a P3 1GHz processor. All of the other HD cards seem to use software decoding which would require a little or a lot more processing power, depending on the card.
As ThomasC says, the MyHD will give you the best playback with a sub 3GB P4 because it"s hardware based. If you cannot get a 1080i or 1080p desktop, the MyHD will output a 1080i signal directly to the TV. And it uses little systems resources while playing back.
I have two MDP120's and one MDP100. The 120's both record in the back to the HTPC in the front. The 100 is used strictly for playback. Since the files don't lock, I can watch them as I'm recording. It also has dual tuners.
The Silver Sensors are good, but you may be fiddling with them forever. I use a Radio Shack powered antenna with dual outputs and programmable channel and antenna position (there are 12 positions total). I can get everything except CBS, which is okay since I have a Silver Sensor for that.
1080i (30 fps) and 720p (60 fps) have the same number of pixels per second, and most of the stations transmit 1080i for convenience. In fact, around here they upscale everything, with the result that you can't do your own aspect-ratio management (4:3 480i upscaled to 1080 and hard-windowboxed into the 16:9 frame is just plain mean). 720p is a little easier to compress, but MPEG-2 is optimised for interlace, so it's a tossup.
Now, "Robust VSB", which is intended to compensate for the well-known fact that digital transmission doesn't fail gently like analog, is going to take a big chunk of that bandwidth away. We'll see what happens then.
I think I've gone through 4 different powered antennas from RS before settling on this one (it's great that RS will take your stuff back for a full refund). The Silver Sensor generally worked, but after a few weeks of solid reception, the reception would just bottom out inexplicably, requiring me to fiddle around with positioning to get it back. One time, NBC was so untunable that I assumed there was a problem with the transmitter for a week. There wasn't.
You're going to probably nee to play around with antennas and amps before you hit the sweet spot. Dual tuners is great for OTA because you can have two antennas pointed in different directions to cover all the bases.
One negative about the MyHD for you is that you need to buy the DVI daughter card. The native output is VGA.