Ok, I have a Gigabyte GA-ex58-UDR3 motherboard, but actually I think
that this question is pretty generic and would apply to almost any
modern motherboard.

I have a SATA hard drive, connected to a SATA port of the Intel ICH10R
chipset [actually, I have two SATA hard drives, and two SATA optical
drives]. The motherboard has a "Gigabyte" IDE/SATA controller on it
(which is actually a JMicron device, which Asus also uses on some
motherboards) to provide an IDE port (and additional SATA ports) but
since I have no IDE devices, that device is disabled entirely in the
BIOS. So it's not part of the question or issue.

Here is the question: The BIOS has two settings for the modes of the
SATA ports (in the Intel ICH10R):

SATA RAID/AHCI Mode (choices are Disabled/Raid/AHCI; set to disabled)
SATA Port 0-3 Native Mode (choice are native/legacy, set to native)

And the system works fine. But it's using "IDE Emulation" to access the
hard drive.

So I set the SATA RAID/AHIC Mode to AHCI .... and the system won't boot.
It crashes during bootup, which causes a loop of continuous resets.

FWIW, I was pretty sure (certain, really) that when I installed this
system (Windows XP SP3, by the way), I used an F6 floppy driver to setup
the system.

So the question: I'd really like the SATA ports operating in AHCI mode.
How do I get there WITHOUT doing a total reinstall of Windows? I
thought I had the necessary SATA driver installed (via the F6 driver I
installed when I first configured the system), but apparently not. So,
again: What do I do to convert the system from accessing the SATA hard
drives via IDE emulation to accessing then in native SATA AHCI mode,
again, without having to reinstall Windows.

???