the Southbridge is the chip that controls all of the computers I/O functions, such as USB, audio, serial, the system BIOS, the ISA bus, the interrupt controller and the IDE channels. In other words, all of the functions of a processor except memory, PCI and AGP.
It appears with the newest bios the prior problems have been sorted out on the Asus A8R32-MVP Deluxe Crossfire (Socket 939) PCI-Express Motherboard. If going crossfire get that mobo.