You don't need the TOP DOG video card to do this. I can't comment on actual performance experience for lower card since i always use the high end card(i.e. now crossfire 4890). TO EMPHASIZE YOU DON'T NEED HIGH END CARD FOR THIS.
+1 to the Hauppauge HVR-2250. I use it in combination with a HVR-1600 so I can record 3 HD and 1 SD signal at the same time. The HVR-2250 is an excellent tuner.
Your graphics card has nothing to do with recording HD content. You don't need a very strong GPU to display HD content, either. I use a lowly 2600XT that I got for $5 after rebate in my HTPC and it works great with 1080 HD recordings.