I have 9800 pro working on Asus mobo-A7VX-X. I did have problems(BSOD and AGP 8X issues) intially when getting both to work together. Tried the works, clean install Win2000,replaced card,checked RAM, Drivers, 4in1s etc etc etc.
In the end went through Via forums. They provide the chipsets KT333 and KT400(which is on mine) there is def a theme of problems with Via chipsets and ATI cards. The support from ATI not great, in the end I found that the way I solved the problems was updating Bios. I had been reluctant to do this but now card and mobo working good.
I understand that there all the 9xxx ATI cards do have issues with Via chipsets (those up to KT400)I would suggest that you do some further research and await for forum members here more knowledgeable than me for advice.