What chipset do you have on your mobo. I had a load of problems with conflicts between a via chipset (KT400) and my 9800 pro (went through considerable pain and troubleshooting).
(drivers/4 in 1s/reformat/directx/ etc etc)
Although I didnt get misread of memory. Have you checked the AGP settings in your bios?
There are some known issues with some of the older via chipsets and some of the 9600-9800 cards.
I solved my problems by a bios update.