If you can't find a driver
that will work with the old hardware, you will have to use a USB connected sound "card".
I used to do a lot of support on the Dell forums and users that upgraded systems to Windows 7 that were not supported by Dell (or other drivers
) were faced with this problem and those that wanted sound either installed a Win 7 compatible sound card in desktops or went the USB device route with laptops.
In a few (very few) cases I've seen some sound functions if the sound driver was installed in a Windows XP compatibility mode. Vista/Win 7 handles some sound functions differently than XP and the reason Vista/Win 7 drivers are needed for full functionality. It probably won't work but worth a try.