SiS and VIA are both gearing up for a launch of Vista-compatible chipsets, both with native support for Direct X 9.0 for the video components, which Vista of course will require to be able to make use of the newer display enhancements. SiS will be offering the SiS770 and SiS670 for AMD and Intel processors respectively, the AMD chipset being available 1Q 2006 and the other during 3Q 2006. Vista is not due for release until the end of next year, giving plenty of time for SiS to supply the market. VIA will be offering the PM890 and K8M890 chipsets around the same time, early next year.
Both of those vendors will feature, at least in particular configurations, onboard video, which Microsoft has mentioned that people should move away from. That isn't exactly easy when the majority of offices make use of it, but with hardware DX9 support in chipsets from Intel, VIA and SiS who by and large produce an overwhelming majority of integrated video for newer boards, Vista should have some wiggle room.