first, being the acer is returned this entire post is moot. This may also come off as a rant, I apologize. I has a PMS.
with that being said.
AHCI or IDE modes have nothing, at all, to do with the CPU. This is for both AMD, Intel, or any other cpu.
AHCI or IDE modes are suported by the hard drive controller. This is typically found in the southbridge of the the chipset. The actual southbridge can differ from an intel ICH7, or ATI SB400, or SB600, or AMD chipset, or VIA, and the list goes on and on and on.
Second, Acer does
support ACHI on some models so the persons in the "know" don't really know. Most Gemstones, Extensas, and Blu's will support AHCI mode as an option in the bios. Some earlier models will require a bios update to enable this option. Acer did not do this to prevent downgrades. You can run AHCI mode in XP, you just have to know how to press the F6 key when you are installing XP to install the Sata drivers from a floppy drive (yes, I said floppy. USB can do wonders). Otherwise, users can just run IDE if they don't know how.
Third, Why does anyone running a laptop need AHCI? Sure it's nice to run in native sata mode, you get hot swap capabilities, and you even get NCQ. However, who would honestly be hot swapping a hard drive in a notebook? Also, how many 2.5 inch hard drives will even support NCQ, not that many. Sure 3.5 inch drives support it, but most laptop drives don't. Even if they do, NCQ does not provide the performance boost that most people think it does. Due to the way it can write data, this would probably also kill battery life in a laptop as well.
And to the amateur intarweb boffins...yes I know sata can support 1.5Gbps, or 3.0Gbps. But, once again, how much transfer can you expect out a 2.5 inch 4200rpm drive, even a 5400rpm drive? Yes I know there are 7200rpm 2.5inchers, I have one. Yes it is faster, but I have not seen transfer rates even pushing 133MB/s on an ATA6 interface. And once again, I realize there is the velociraptor 10,000rpm 2.5 inch drive. Try squeezing that 12.5mm high drive into your laptop, doubt it fits. not to mention the heat output....