I have an older desktop sitting around that's 2.3 gHZ I believe and 2GB of RAM and I can stream in HD/HQ with no issues at all. I do have a very fast network, but this PC isn't that great and it can handle it. I can't recall which video card is in this one but it may be a middle of the road card, but not anything extreme by any means.
Now that I think about it, I think the video card brand or model is called Extreme actually, I forgot that I see a green screen flash on boot displaying the work Extreme,