I have successfully enabled AHCI under Windows XP on my P35 based motherboard (Abit IP35 with ICH9R) using these instructions and I have tried to do the same to my P45 based notebook (Samsung R560 with ICH9M) but the problem is after forcing AHCI in the BIOS Windows XP doesn't even attempt to boot. I have Linux Mint installed as well with GRUB being the boot manager and Linux works fine and detects ICH9M in AHCI mode. After selecting Windows XP from GRUB, "Starting up..." appears and that's it, even after 15min of waiting nothing happens. The notebook itself came with Vista pre-installed and it worked in AHCI mode there so why doesn't it want to work under XP? The BIOS even has an "Auto" setting that will set AHCI mode according to what OS is being booted - for XP it will be disabled and for any other enabled. Maybe the BIOS is somehow broken and doesn't boot XP properly in AHCI mode? I have basically tried every combination of, somewhat limited, BIOS including EFI boot, legacy disk access mode, but it still doesn't even try to boot XP. On the manufacturers site there is a BIOS update but it says that mine is already newer so it quits without doing anything. I'm using 32-bit version of XP even tho the system is perfectly capable of running a 64-bit version (having P8600 and 4GB of RAM) so maybe that's the problem? Mint is 64-bit. Edit with solution: The solution to my problem came somewhat unexpectedly... Windows 7's bootloader is able to boot Windows XP while AHCI is on so I think Vista's might be able to do it as well.
