XP Supports AHCI just fine. You have to download the Intel Matrix floppy driver from Intel's site and load it during setup when the message "Press F6 if you need to install a third party SCSI or RAID driver" appears. I've had AHCI working fine in XP, Vista and Windows 7, and both 32-bit and 64-bit versions of each.
As I recall, it'll look for an 'internal' floppy drive, it won't see a usb floppy drive-
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