The South bridges are called the MCP-S and MCP-S1000, and they will probably look like this: Eight USB 2 ports, nVidia RAID (RAID 0, RAID 1 and RAID 0 + 1), Gigabit Ethernet, 2 Serial ATA ports.
Early samples of this chipset will now make their appearance in October, and boards powered with it could easily be available at the end of that month or perhaps more realistically, the beginning of November.Source : The Inquirer
Motherboard manufacturers are ready for this chip as their design is already finished. It's up to Nvidia now since it is the one to delay this product.
Nvidia is very close to having its Nforce 3 boards in retail, but we reckon you wont be able to get these boards before late September -- at least for the Athlon 64 versions since the CPU won't be announced before the 22nd of September.