When I upgraded my Dell Dimension 8300 to Windows 7 Pro32bit a couple years ago, according to everything I tried and googled, it was impossible to get the onboard audio ports working, as no drivers existed.
I'm posting the happy news that a few weeks back Windows Update rectified that, and now onboard audio IS working on my Dell Dimension 8300!
(I can't post details, sorry, since I don't see it in "Installed Updates".)