Well after three weeks of trying everything (suggested by posters here) from
using default IDE drivers, to disabling USB, taking out the sound card,
replacing ram, etc etc, I've sent back my SATA II drive for a
repair/replacement.

Regardless of what I'd do, when the SATA controller was enabled on the
motherboard, WinXP Sp2 would take several mins to boot, and on the occasions
when the drive was actually recognised and it did, I would get :

The driver detected a controller error on \Device\Harddisk0\D.
For more information, see Help and Support Center at
http://go.microsoft.com/fwlink/events.asp

Along with :

The device, \Device\Ide\IdePort3, is not ready for access yet.
For more information, see Help and Support Center at
http://go.microsoft.com/fwlink/events.asp

The drive would then click twice, and hang the entire system.

I'm back on an old UDMA drive for Windows XP, but this has to be one of the
most frustrating issues I've ever experienced.
Would be grateful to know if anyone has had this same problem with the
GA-K8NXP-9 and whether I'm going to have the same hell when I get the
replacement SATA-II drive back.
Thanks!