although a dual core processor will function in an entertainment system, you can probably see better video quality with a quad core processor, DDR3 memory, PCI16x video card, (not on board video), I prefer a high end video card such as ATI 5870.
Now some people would say that it is crazy to go through all that quad core stuff to watch video. I think, after comparing the cheaper to the more expensive, that the extra money was worth it in video quality and sound quality. (many of the quad core boards have surround sound on board)
I compared the high end video card to the less expensive, and I thought the quality was noticeably better with the 5870, especially watching streaming video.
So if I could pay for it I would go for the quad core.