The first source of drivers would be the manufacturer of your computer.
If it is say a Dell Dimension 4200 then go to the Dell web site under support download drivers
Plug in your model and look for the Audio driver.
If you computer is custom built then you want to follow the same steps at the site of your motherboard manufacturer.
Plug in your board model and the driver will be there.
If you need to ID your board you can run this scan:
http://www.d-a-l.com/hardware-scan.php