I want to replace the onboard audio with a SoundBlaster card, but first need to disable the onboard audio. I could find no provision for that in the bios, so don't know how to go about disabling the onboard sound. Sure hope someone can steer me in the right direction!

Go to the mfg of the mother board website and see if there is any support
Go into control panel and then system properties, hardware tab and click device mgr
In device mgr, go down to sound devices and find the driver for the ASUS and right click on it and then choose Disable

Hope this helps

First, uninstall the onboard controller in the device manager. Then enter BIOS and disable the onboard AC97 controller under Advanced > IO Device Configuration. Page 2-22 of the board's manual downloadable from Asus' web site provides additional info.

Thanks Seahwk and Scloros, my new SoundBlaster is now working!