It's a good job you're sensible, that advice was meant for someone else with similar probs, but with an Intel pc. All I can do is apologise and hope you accept my apology.
After setting your BIOS to AHCI; You should follow carefully the instructions in section 5-1-2 of your Manual, before going on to the actual installation of the AHCI drivers covered in section 5-1-3.
When you receive the errors that you have been receiving, you should make a fresh set of Floppies from your Motherboard Disk.
Sorry this is taking so long, you're original post had you installing drivers first for XPx86 and then for XPx64 which confused me for a long time.
Download an updated Manual from here....
Your problems are not unique, Phil, but from what I've learned it's all about making clean and fresh floppies for the initial set-up.
Shame you aint installing Vista, you wouldn't need to do all this. lol.