after searching around the forums it looks like that x8 AGP does not work with some SIS/VIA combos. Tbreak in their review was not able to get it. I heard that you can get ahold of ATI and get a newever version to work. On another thread over the
Spent over an hour with ATI Customer Service Canada and more important, the Engineering Dept. The subject: Our testing shows the Radeon 9700 will NOT work at all on the Asus P4S8X (SiS648), Gigabyte 7VAXP (KT400/8235), and VIA P4PB (P4X400/8235) which are the only 8x AGP boards on the market. Customer Service was not completely aware of this, but Engineering is.
According to ATI, they are now receiving and testing these 8X AGP boards. They are ALSO finding the 9700 does not work at all or works intermittently at best on these boards. Engineering indicated most of the boards already shipped have this problem.
Solution: A new BIOS and some board revisions are now available that fix this problem. Call ATI Customer Service for help with the issue. At present, they will ship a replacement board that WILL work in SiS and VIA 8X, but they are also considering a BIOS flash solution for problem boards.
Customer Service and Engineering deserve a 10-1/2 for their wonderful handling of this issue. They are very concerned that it be corrected quickly. They also shared that most of their 8X validation testing was done with Intel's unreleased 8X chipset and that they are just now receiving shipping versions of the SiS and VIA 8X chipsets.
You can find tons of other info if you do a search at rage using the KT400 as that is the chip set on your KT4 Ultra. Good luck!