The chipset drivers for the nForce 3 motherboards are available on NVIDIA's driver download page.  Here you will need to select "Legacy" under Product Type, select "nForce 3 Series" under Product Series and select your operting system then click Search.

The audio drivers for the nForce 3 motherboards are available on Realtek's download page.  Here you will need to select "AC'97 Audio Codecs" and then agree to the terms and conditions to download the drivers.  Here you will be able to select the correct driver for your operating system.