the recording is done in software. the tuner card output and your computer will determine the quality and size of what could be recorded.
you need to determine if that quality and size will give you what you want.
if you wanted to record shows you could also consider a video recorder (stand alone, not connected to computer) like a Magnavox MDR533H or MDR535H. these have a hard drive in it to record or view from. you can archive the recording to a DVD (even a rewritable type).
Check with the manufacturer’s web site for the product manual of any tuner card you are considering. Some include PVR software, some don’t. Even the best tuner card PVR software isn’t for everybody so some people bite the bullet and install something like XBMC.
Here’s a listing of the more common PVR (and more) software packages.
Generally, cards have a single tuner. So you can’t watch one program while recording another. But dual tuner cards do exist. Just be very careful that you can, for example, tune in to two HD channels at the same time. (Some might allow only 1 SD and 1 HD. Or one uses a tuner and the other uses HDMI/Compsite/etc. input.) Again, check the docs on the manufacturers web site.
If you get a card with full hardware encoding/decoding, then the load on the computer isn’t too bad. If one or both tuners uses software encoding/decoding, then you better have a really fast, dedicated computer.
Sites like AVS Forum are good place to check out for hard core tech discussion of this.
Thanks for the info, ftg. I’m using a Hauppauge dual tuner on my PC now, and it seems to work alright, but your links should be good for helping me resolve an annoying stutter that’s developed during playback sometimes. Other than that, and needing to buy HD rabbit ears, it’s worked like a dream and serves as our TV today.