From my personal experience I've been able to just install the alternate card and the BIOS will disable the onboard sound automatically.
However I have also encountered boards that require you to disable them in the BIOS , just like a few people have already mentioned. :cool:
You dont have to do much in the operating system at all, just remove the drivers because the OS should remove the device, it will not load a device into the device manager if it is not present. ;)
