Execute the following command to install the necessary build tools and gcc-3.4. Ubuntu 5.10 uses gcc-4.0 by default but the kernel is compiled with 3.4.
sudo apt-get install build-essential gcc-3.4
Now run the installer with the following commands.
sudo sh NFORCE....
Sound and ethernet work for my Gigabyte k8nf-9 nforce4 motherboard with the snd-intel8x0 and forcedeth modules provided with the Ubuntu kernel. Don't they work for you?