Here's an update. I downloaded and installed the following drivers:

Chipset/platform
VIA Hyperion 4in1 drivers version 455vp1

Video card
Radeon Omega drivers version 2.6.05a (Catalyst 5.1)

IDE controllers
VIA IDE Accelerator driver version 120b

Now the audio stutter has stopped, but I still can't burn CDs. Thanks for your input so far, at least we solved one problem.