comcast high defintion cable channels through a tuner card?

i'm getting confused. i'm beginning to think that what i'd like isn't possible.

can i get a tuner card which can play high definition channels from cable? not my local news channel, but espnhd for example?

thanks.

this is what i'm gathering as well. the only way to get espn hd then is to buy a pre-built computer from a few select companies (who still buys pre-built if they want a good computer?) or to have a tv that already has one built in?

my understanding is i can buy one of these ati digital cable tuners but there is no way to make it work without the above said pre-built. is this really true? only local channel hd content on pc's still? then what is an htpc and what is media center for?

should i just buy a good tuner card of some sort from hauppauge then and watch local hd through the comcast box and wish for the day that i can watch their other channels hd? i have to pay extra to get their channels in hd and pay extra to get a separate set top box for hd, but then i'll still only be able to watch the local channels in hd???