I came across this again today and thought it might be useful for somebody.
I was installing Windows XP Pro (OEM) on a HP nx6310, so I instered the XP CD and booted from it fine. Setup started ok, but then hit me with “Setup did not find any hard disk drives installed in your computer” – doh!
In the end the fix was easy. Enter the BIOS (F10 at startup) and change the “SATA Native Mode” to Disabled. Next time setup ran, it found the disk and installed XP with no problems. Simples.