In all actuality you want to go with, well lets say an ATI x1800xt (i have one) and then get a tv tuner seperately, thats what i have in my video rig. And my reasoning for this would be as follows: having a video card/tv tuner on the same pciexpress board puts more strain on A)the pci-e slot, b)puts more stress on the card itself, and c) it crushes performance on both devices!!
So just get them seperate!
Mac G5 workstation with 4 gigs of ram, 4x250 gig drives in raid 5. High availability cluster server running centos for a server. 2xCanon GL2 cameras.