sbiddle:rixth: sbiddle: keep in mind that the 780G has been praised for being an excellent http://www.silentpcreview.com/article807-page8.html
Playing this clip: http://www.apple.com/trailers/newline/rushhour3/hd/ (1080p | 24fps | ~10mbps) used only 12% of the CPU when it was underclocked to 1.5ghz. I can't imagine TV 3 is going to be 9 times as demanding.
Maybe not 9 times - probably about 10x more demanding! Our H.264 broadcasts are nothing like the QT trailers.
If you go down the ATI path it's at your own risk - there are know issues with all ATI 2xxx/3xxx cards and even the 780G chipset with hardware accelerated H.264 interlaced content. I've spent hundreds of $$ trying various combinations before I realised an Series 8 or 9 NVidia (8500 or greater) is the only way to go. If you buy ATI I just about guarantee it won't work well.
Or it will work just fine. (GA-MA78GM-S2H)
Oh, and the Athlon 4200+ x2 can do TV3 without hardware acceleration and if you aren't doing anything else it won't drop frames, but it will have a big jitter so it's not quite smooth but perfectly watchable, it shows at about 50% CPU usage on average (over both cores).
I will admit though, sometimes i'll change to a channel, one of the low def ones especially and it will be corrupted, switching channel or rebuilding the graph will fix it. Sometimes corruption spreads to Vista Aero.