Hey, AudioDoc --
I stumbled onto this thread a few days ago, whilst attempting the same thing you were trying back in the fall, and wanted to share my own tale... and see if you have any further insights to share.
Both machines in question are AMD-based, so a lot of the advice out there, being Intel-based, won't work. So it takes a little more digging to find the answers. I've effectively been trying the IDE-to-AHCI conversion on three
different OS versions, and have had success on two, and partial on the other. As you might guess, XP is the "partial" success. My wife's machine is running Windows 7 64-bit, and I installed it in IDE mode before I knew better. But switching it to AHCI was
relatively simple, took me about an hour of nervously picking at the registry, installing some drivers, etc. At the final boot, everything loaded up like magic. I have had nothing but good experiences with Win 7, it seems to be very nimble at seeing what
it needs to do.
My own machine has both Win XP and Win 8, and they've been tougher. I converted Win 8 first, which took some more extensive registry editing, but now that appears to be fine, as well. However, I would have to switch the BIOS back to IDE mode, if I wanted
to boot into XP. Unacceptable, so I started picking at making that AHCI-compliant, as well, and here's where I ran aground. After much searching, many driver downloads, many registry hacks, many restores, etc., I have XP able to run with the BIOS set to
AHCI. However, the ahcix86.sys driver (the only one which seems to be recommended for XP) insisted on installing as "AMD AHCI Compatible RAID Controller", under SCSI Devices. But under IDE ATA/ATAPI Controllers, I cannot seem to get that driver to take.
I had to force it to even show a SATA controller at all -- an AMD SATA controller, using a Win 7 driver -- and that is all it will do. It sits there with a question mark over it, and the OS still apparently runs in IDE mode.
I've about reached the point where you did, though, and am about to give up on it... not that I want to re-install anything, I'm only continuing to use XP long enough to get cozy with Win 8, and I'm almost there, after several tweaks. And I don't need
TRIM support in XP, that runs on a HDD, unlike Win 8, which I have on an OCZ SSD. My only goal was to make it so that I didn't need to flip the BIOS each time I wanted to boot into a different OS, and I've accomplished that. Eventually, I'll just uninstall
XP and run with Win 8. So I guess the moral of the story is... there's only so much time you can fiddle around with something that's outdated!
Regards,