Dell used 2 different sound chipsets in the Dimension 3100.
STAC 92XX C-Major HD Audio File name: R114282.exe
and
Creative Labs Integrated Audigy invitation File name: AP0SRC4.zip
Dell does not post non-working drivers. Please use the one that matches your hardware. If you then have a problem, please include details of where it fails and what error messages you get along with a detailed description of what is listed in Device Manager under Sound.