This how-to is very old. If you have this sound card and sound is not working for you with the latest version of Ubuntu (currently 10.04) this guide will not help you. Please file a bug report on Launchpad.
If you are going to upgrade to Ubuntu 8.04 Hardy Heron you will notice that it will want to remove the linux-backports-modules package. This is OK. Doing so will not affect your sound since it now works out of the “box” with 8.04. :D
There’s currently a bug in the latest stable version of the ALSA drivers (1.0.14). There is no sound with a HDA Intel ICH8 Family (rev 03) sound card.
00:1b.0 Audio device: Intel Corporation 82801H (ICH8 Family) HD Audio Controller (rev 03) Subsystem: Hewlett-Packard Company Unknown device 30cc Flags: bus master, fast devsel, latency 0, IRQ 23 Memory at f8500000 (64-bit, non-prefetchable) [size=16K] Capabilities:  Power Management version 2 Capabilities:  Message Signalled Interrupts: Mask- 64bit+ Queue=0/0 Enable- Capabilities:  Express Unknown type IRQ 0
There was no sound in Feisty and the only way to get it working was to compile ALSA with the special instructions here along with a custom patch for the Realtek codec which you had to go digging through the ALSA bug tracking system to find. Anyways a lot of work to get sound working in Feisty.
But now that Gutsy is out, there still is no sound out of the virtual "box". :P However, getting sound to work is extremely easy now. The issue was fixed in the latest development version of ALSA (1.0.15rc3), but Gutsy ships with 1.0.14. Compiling ALSA is not necessary to get sound working anymore. In fact, doing so would only cause more problems due to the fact that when you compile ALSA, it places a module in one place while Ubuntu has that same module, but a different version, in a different place causing a bunch of conflicts and in the end, no sound.
So in order to fix this all you need to do is open the Software Properties, go to the Updates tab, and enable the Gutsy Backports.
Click the Reload button when prompted.
Then just run this command
sudo apt-get install linux-backports-modules-generic
If you are running a different kernel, such as the i386 kernel, replace generic with i386. The default install uses a generic kernel. Reboot and you should have sound working. :D
The reason it works is because that package contains ALSA 1.0.15rc3
This worked for me on an HP Pavilion dv6500t laptop
(Edit: Gutsy Proposed Updates is not needed for this.)