A "Realtek High Definition Audio Driver Update" is listed here, a 13MB file.
That is the only HP file that looks reasonable to solve a sound problem. 126.96.36.19923
You can look for the latest ReakTek driver here. R1.91 = 188.8.131.5205
"Windows 2000, Windows XP/2003(32/64 bits) Driver only (ZIP file)"
KB888111 UAA driver is here, if that seems to be missing. You can try
installing this first, and then try the ReakTek driver afterwards.
To make HDaudio work, you need the UAA driver from Microsoft (one may be
included in the RealTek or HP packages, or you can get the file separately).
Then, the hardware driver component is also needed (as it contains registry
entries that map the jack configuration to the hardware).