The major advantage of RS400 over RS350 is the adoption of a real DirectX 9 IGP. Even though RS350 utilizes a Radeon 9100 Pro for IGP, it is still technically DX8.1. RS400 will integrate the Radeon 9600 Non-Pro GPU onboard, which should give Intel's 915G a run for its money. If ATI's roadmaps are to be trusted, this is a bit of a surprise for us. Our original roadmaps in April market RS480 to launch with DX8.1 instead of DX9. Unfortunately, graphics performance is only the secondary function of an IGP chipset, and thus the northbridge must be up to snuff. ATI's memory controller has been its downfall many times before in the past.
http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2134
Looks interesting . 9600 gpu on board video would be a very nice jump over the nforce 2 intergrated video and intell intergrated video