Disable onboard and use anything else. PCI and USB sound cards are too cheap for me to futz with onboard. Examples at http://www.geeks.com/products.asp?cat=SND
Maybe free at freecycle (see google.com)
I have an older Dell Dimension E510 which I recently wiped & installed Windows XP. It didn't have any sound drivers, so I downloaded the SigmaTel drivers from Dell and installed those.
(Side note: I installed the chipset drivers after the sound drivers initially, but then I uninstalled the sound driver fully and reinstalled it.)
The SigmaTel drivers work...sorta. The sound is there, but it cracks every now and then, cuts off, and on low-quality, old speakers, the sound is muffled when you first play it (but that could be the speakers).
Any suggestions on how to fix this busted driver? Thanks in advance.