strictly speaking, the chipset on a64 boards handles the interface between the peripherals, since the memory controller in all K8 CPU's connects directly to the memory. (K8 CPU's include all socket 754, 939, and 940 CPU's, including Semprons, Athlon64, and FX)
Chipset is responsible for IDE control, onboard sound, onboard video, onboard ethernet, among other things. Probably the most important job for K8 chipsets in the interface for graphics, like AGP or PCIe.
SiS isn't really a top tier model, but it should get the job done.