Hi DJ,
I can not see amdsata.sys and amdxata.sys in the package downloaded from http://support.amd.com/en-us/download/desktop?os=Windows+XP+-+Professional/Home under "Optional Downloads".
In these folder, I only see ahcix86.sys, amd_sata.sys and amd_xata.sys.
Do you know the link to download amdsata.sys and amdxata.sys ?
You need to download both the chipset drivers and the RAID drivers. I believe the complete list was assembled from the two download packages.
Since I did this, in the spring of 2013, it looks like they may have streamlined the process a bit... The two download packages I see now are executables, which may make this easier if the drivers are self-installing... you may not have to follow my method at all. Try this link: http://support.amd.com/en-us/download Then go down to the section that says "Manually Select Your Driver".
-- under System, select Chipsets
-- under Product Family, select your chipset series (mine uses the 780 chipset and 700 Southbridge, so I selected "7 Series"
-- under Product, select "All" (mine was "All 7-Series Chipsets")
-- under Operating System, choose XP 32 or 64 bit (the exe's are the same for both, it probably contains two sets of drivers and uses the ones it needs)
-- download both driver packages, and run them.
Afterwards, look at your Device Manager. If you don't see "AMD SATA Controller", then add it with the Hardware Wizard, and install the registry hack, the way I described it. (You may need to install the registry hack, regardless.) But once you have that device listed, and its Properties say it's installed correctly, you should be able to reboot into BIOS and flip the switch.