I experience graphics and video online. I have the thought that I may not being using DVDs or programs with 3D graphics, but you need a computer that can handle what is up to date when browsing and visiting sites on the internet.
Yes, the online HD playback is very heavy and requires very fast PC, but every _new_ pc will handle it.
Latest graphics cards support ofload of HD video decoding (as well DVD's and Blue Ray), however this is not working stable yet and it's not official - adobe needs to release their flash player 10.1.
Anyway, the CPUs can handle it as well pretty much fast. Graphics cards are like 3-5 times faster in doing it and they leave lot's of cpu cycles for use, but this is not working yet (it's crashing on my nvidia 240M).