Do a clean driver installation. Follow
these instructions. When purging the inf files be sure to search for and delete the files drvdata.bin and drvidx.bin from the C:\windows\inf and/or C:\windows\inf\other directories. When your system is prepared for new drivers, follow the manual installation found
here. For bios setup and irq issues look
here. If you install the MMC after drivers the installation will overwrite the Via AGP gart with the ATI gart. Cure this by using msconfig and unchecking ATIPOLAB from startup menu. Restart and reinstall just the Via AGP gart in turbo mode. Before you do any of the above use regedit and make sure the HyperZ hack is enabled as that may be all you need.
Registry info link.