Realtek High Definition Audio doesn't install properly

I have a problem installing Realtek High Definition Audio drivers.
When installing the most recent driver from Realtek website
(WDM_R178.exe), the driver installation stops with an error message:
Install Realtek HD Audio Driver Failure !!

When I look at the device manager, it says that the drivers are not
installed.

I'm using an ASUS P5K motherboard with onboard audio enabled in the
BIOS. Also using WinXP Pro with all the latest patches.

At some point, I decided to disabled the audio device within the BIOS
and I was able to fully install the driver from Realtek, but if I go
back and re-enable the onboard audio.. still the same issue, no sound
and the device manager still show a problem with High Definition Audio
driver.

I also tried to uninstall the High Definition Audio driver from the
device manager, but I'm getting an error saying that it's not possible
to remove it because it is required for booting the OS.

I saw a couple of threads on similar issue, but can't find a clear
solution for that.

Please help me with this issue.

Thanks.

Jeff.