No audio & 'Unknown PCI Device'

I've installed a clean Windows XP on a new computer, using the following steps:
1. Windows XP + SP2 + SP3
2. New computer's drivers

However after finishing the audio didn't work, I had 'Unknown PCI Device' listed in my device manager and no audio device in the audio devices list. In the system devices there was no Microsoft AAU device.

I tried many things: check bios settings, update the bios, reinstall RealTek drivers... nothing helped.

The solution I found on one forum stated that there is a problem with Windows XP SP3 HD Audio driver. F**k. Why Microsoft? WHY?

Anyhow, the solution that worked for me:
1. Impersonate to WinXP SP2: Change registry key
"HKLM\SYSTEM\CurrentControlSet\Control\Windows\CSDVersion" value to 200
2. Restart
3. Install HD_Audio/kb888111xpsp2.exe
4. Install RealTek HD Audio driver
5. Restart (and check that the audio is now working)
6. Change the CSDVersion key back to XP SP3 again:
"HKLM\SYSTEM\CurrentControlSet\Control\Windows\CSDVersion" value to 300