Well you probably want to go with a seperate video card and sound card if you want really good video quality and sound quality. That Radeon 7000 I linked to earlier would be just right. ATI cards have better 2D quality than Nvidia. The best 2D quality, however, would be a Matrox card but they are expensive.
THIS motheroboard would be a good replacement. It has an Nforce 2 chipset which is about as good as it gets for AMD. As for the sound card, if you are a big audiophile but don't need any surround sound then
THIS M-Audio sound card is excellent. If you don't want to spend that much or you want all the frills of surround sound and other features then a
Sound Blaster Audigy 2 ZS is a great choice.